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George   Davidson 
i  <~n  i 


HOW  TO  USE 


THE 


ANEBOID   BABOMETEB 


BY 


EDWARD  /  WHYMPEE 


I.  COMPARISONS   IN  THE  FIELD 

II.  EXPERIMENTS  IN  THE  WORKSHOP 

III.  UPON  THE  USE  OF  THE  ANEROID  BAROMETER 

IN  DETERMINATION  OF  ALTITUDES 

IV.  RECAPITULATION 


NEW    YORK 

CHARLES  SCRIBNER'S  SONS,  743,  745  BROADWAY 

1891 


All  rights  are  reserved 


GIFT 


ZOOLOGICAL  COLLECTIONS 
FROM  THE  GREAT  ANDES  OF  THE  EQUATOR. 


WALTER  BURTON,  Naturalist,  of  191  WARDOUR  ST.,  LONDON,  W., 

begs  to  inform  Collectors  of  BIRDS,  INSECTS,  REPTILES,  and  FISHES  that  he 
has  the  collections  formed  l>y  EDWARD  WHYMPER,  Es^.,  upon  his  Journey  in 
Ecuador  for  sale,  including  : — 

The  first  set  of  the  DIURNAL  LEPIDOPTERA,  classified  in  14  boxes,  embrac- 
ing 240  specimens  of  106  Species,  taken  at  various  elevations  up  to  16,000 
feet  above  the  sea,  with  Localities  and  Descriptions  attached  ;  duplicates  of 
Colias  dimera,  Doubl.  and  Hew.,  Picris  xanthodue,  Lucas,  Pieris  elodia,  Boisd., 
etc.,  Is.  6d.  to  2s.  each  ;  numerous  skins  of  Humming  and  other  BIRDS,  in  the 
very  best  condition  ;  excellent  specimens  of  the  very  rare  and  interesting  FISH, 
Cyclopium  cydopum,  Humboldt  (see  Travels  amongst  the  Great  Andes,  chap,  xii, 
and  the  description  in  Supp.  App.  by  the  late  Dr.  F.  Day),  4s.  to  7s.  each  ; 
amongst  the  FROGS  perfect  examples  of  males,  females  and  young  of  the 
curious  Nototrema  marsupiatum  (Dum.  &  Bibr.)  ;  also  of  the  new  species 
Hylodes  IVTiymperi,  described  by  Mr.  G.  A.  Boulenger,  captured  from  11,000 
to  13,200  feet;  Hylodes  conspicillatus,  Gtlir. ;  H.  unistriyatus,  Gthr.,  and 
young;  Phryniscus  Icevis,  Gthr. ;  Dendrohates  tinctorius  (Schneid.) ;  Bufo  ayua, 
etc.  etc.,  3s.  to  7s.  6d.  each.  Fine  specimens  of  the  LIZARDS  Liocephalus 
trachycephalus,  L.  iridcscens,  Gthr. ;  Ecpleopus  (Pholidobolus)  montium,  Peters  ; 
etc.  etc.,  5s.  to  7s.  each.  Examples  of  the  SNAKES  Liophi's  regime,  L.,  var. 
albiventris,  Jan. ;  L.  splendent,  Jan. ;  Bothrops  atrox,  (L.) ;  R  Schleyeli,  (Berthold) ; 
Leptoynathus  nebulatus,  (L.)  ;  Elaps  Marcyrari,  (Wied.),  var.  ancolaris,  Jan. ; 
Oxyrhopus  clcelia,  Jan.;  Boa  constrictor,  L.,  etc.  etc.,  5s.  to  7s.  each.  Specimens 
of  the  SCORPIONS  Broteas  subnitens,  Gervais  (from  10,000  feet  and  upwards), 
and  Centrums  Americaims,  De  Geer  ;  of  the  AMPHIPOD  Hyalella  inermis,  S.  I. 
Smith  (obtained  from  12,000  to  13,000  feet);  and  the  fine  BUG  Carineta 
basalis,  Walker.  Good  series  of  the  new  species  of  ANT  Phcidole  monticola 
(females,  soldiers  and  workers)  described  by  Mr.  P.  Cameron;  and  specimens 
of  Camponotus  atriceps,  Sm.,  G.  sylvaticus,  Oliv.,  Atta  sexdens,  L.,  Pseudomyrma 
gracilis,  Fabr.,  Edatomma  quadridens,  Fab.,  and  Pachycondyla  carbonaria, 
Smith,  etc.  etc.,  Is.  to  Is.  6d.  each.  And  a  numerous  series  of  the  special 
COLEOPTERA  of  the  highest  zones  of  the  Ecuadorian  Andes,  including  the 
following  New  Species  which  are  described  in  the  Supplementary  Appendix  to 
Travels  amongst  the  Great  Andes  of  the  Equator: — Leucopeltea  albescens,  Bates  ; 
Colpodes  stcno,  Bates  ;  C.  alticola,  Bates  ;  Pterostichns  integer,  Bates ;  Aniso- 
tarsui  bradytoides,  Bates  ;  Pelmatellus  Andium,  Bates ;  P.  variipes,  Bates  ; 
P.  oxynodes,  Bates  ;  Astylus  bis-sexyuttatus,  Gorham  ;  Ananca  dcbilis,  Sliarji  : 
Meloe  sexguttatus,  Sharp;  Sterculia  impressipennis,  Sharp;  Epitragus  (?•//»'//'.<, 
Sharp  ;  Philonthus  Whymperi,  Sharp  ;  Silpha  microps,  Sharp,  etc.  etc.,  Is.  6d. 
to  2s.  6d.  each.  , 

WALTER  BURTON,  191  WARDOUR  STREET,  LONDON. 


HOW  TO  USE 


THE 


ANEROID  BAKOMETER 


BY 


EDWARD    WHYMPER 

H 


I.  COMPARISONS  IN  THE  FIELD 

II.  EXPERIMENTS  IN  THE  WORKSHOP 

III.  UPON  THE  USE  OF  THE  ANEROID  BAROMETER 

IN  DETERMINATION  OF  ALTITUDES 

IV.  RECAPITULATION 


NEW   YOEK 

CHAELES  SCEIBNEK'S  SONS,  743,  745  BEOADWAY 

1891 

All  rights  are  reserved 


I       A 


qe 
W 


PBEFACE. 


THE  following  paper  is  divided  into  four  sections.  The  first  records  com- 
parisons of  the  aneroid  against  the  mercurial  barometer  in  the  field  ;  the 
second  is  concerned  with  experimental  research  in  the  workshop  ;  the  third 
is  occupied  by  practical  considerations  arising  from  the  facts  recorded  ;  and 
the  fourth  is  composed  of  a  recapitulation  of  the  principal  points  which  are 
dwelt  upon  in  the  previous  parts,  and  forms  an  index  to  the  whole. 

The  investigations  which  are  recorded  in  these  pages  have  extended  over 
eleven  years.  In  1879—80,  having  occasion  to  pass  some  length  of  time 
at  great  elevations  in  the  Equatorial  regions  of  South  America,  I  took  the 
opportunity  to  make  comparisons  of  the  aneroid  against  the  mercurial 
barometer  at  low  pressures.  Some  of  these  comparisons  are  given  in  the 
First  Part.1 

On  entering  upon  this  journey,  I  entertained  the  hope  that  close  approxi- 
mations to  true  atmospheric  pressure  might  be  obtained  by  employing  several 
or  a  number  of  aneroids.  The  idea  was  that  the  plus  errors  of  some  instru- 
ments might  balance  the  minus  errors  of  others,  and  that  means  of  the 
whole  might  come  near  the  truth.  This  hope  was  speedily  dissipated. 
Each  individual  instrument  indicated  lower  pressures  than  the  mercurial 
barometer,  and  means  of  the  whole  were,  consequently,  less  than  the  truth. 
Deduced  altitudes  were  much  too  high.  In  strong  contrast  to  these  un- 
welcome facts  there  were  others  equally  perplexing,  although  less  unpleasant. 
It  was  found  that  even  when  the  aneroids  had  acquired  minus  errors  of  one 
to  two  inches  they  might  on  differences  of  level  of  several  thousand  feet  indicate 
nearly  the  same  differences  of  pressure  as  the  mercurial  barometer.  Ascending 

1  Part  1  is  reprinted  from  the  Appendix  to  Travels  amongst  the  Great  Andes  of  the 
Equator.  This  volume  contains  an  account  of  the  journey,  and  describes  the  circum- 
stances under  which  the  comparisons  were  made.  These  two  works  are  published  simul- 
taneously, and  can  be  obtained  separately. 

B 


W 

M294554 


2  PEE  FACE. 

observations  of  aneroids,  it  was  found,  never  agreed  with  descending  ones,  and 
the  latter  always  indicated  less  difference  of  pressure  and  less  difference  of  level 
than  the  former,  if  they  were  made  only  a  short  time  after  them  ;  but,  in 
such  cases,  means  of  the  ascending  and  descending  observations  closely  accorded 
with  means  of  similar  observations  made  with  the  mercurial  barometer. 

A  long  time  elapsed  after  my  return  from  this  journey  before  I  commenced 
to  find  a  solution  of  these  puzzles.  I  examined  and  rearranged  my  observa- 
tions for  several  years  before  it  occurred  to  me  to  tabulate  the  means  of  the 
whole  of  the  aneroid  readings  in  chronological  order,  to  do  the  same  for  the 
readings  of  each  individual  instrument,  and  to  take  out  the  differences  from 
the  mercurial  barometer  of  each  mean  and  of  each  individual  reading.  When 
this  was  done  I  saw  that  the  results  were  influenced  by  the  lapse  of  time 
between  the  readings  as  well  as  by  variations  in  pressure.  The  general  con- 
clusions at  which  I  then  arrived  are  stated  upon  pp.  9,  14. 

Having  introduced  the  matter  to  the  notice  of  Mr.  J.  J.  Hicks,  of  8 
Hatton  Garden,  and  gained  his  co-operation,  I  then  proceeded  to  test  aneroids 
under  varied  conditions  of  time  and  pressure  ;  in  the  end  finding  explana- 
tions for  the  points  of  perplexity,  and  that  aneroids,  whilst  largely  differing 
amongst  each  other,  all  follow  rules  which  have  the  force  of  law. 

The  prosecution  of  these  experiments  has  extended  over  a  far  greater  length 
of  time  than  appeared  necessary  at  their  inception,  and  has  absorbed  almost 
all  my  leisure  during  the  last  few  years.  The  labour  will  have  been  well 
bestowed,  and  I  shall  attain  my  aim,  if  in  these  pages  I  succeed  in  explaining 
some  points  in  the  behaviour  of  aneroids  which  have  undoubtedly  been 
puzzling,  and  have  seemed  contradictory  and  anomalous  ;  and  thus  render  it 
possible  for  the  ever-increasing  number  of  those  who  employ  these  instruments 
in  the  field  to  use  them  with  more  confidence  and  certainty. 

EDWARD  WHYMPER. 


PART    I. 

COMPARISONS   OF  THE   ANEROID   AGAINST   THE 
MERCURIAL    BAROMETER. 


Aneroids  were  carried  to  Ecuador  to  endeavour  to  ascertain  whether  the 
'means  of  the  readings  of  several,  or  of  a  number,  would  or  would  not  accord 
with  the  mercurial  barometer  at  low  pressures. 

It  has  long  been  known  that  the  indications  afforded  by  a  single  aneroid 
are  apt  to  be  of  a  very  deceiving  nature,  even  at  moderate  elevations  ;  but  it 
seemed  to  me  possible  if  several,  or  if  a  number  were  employed,  that  one 
might,  by  inter-comparison,  discriminate  between  those  which  went  most 
astray  and  those  which  held  closely  together  ;  and  that,  by  adoption  of  the 
means  of  the  readings  of  the  latter,  a  decent  approximation  might  be  obtained 
to  the  truth,  possibly  even  at  great  altitudes.  It  may  be  added  that  I  wished 
this  might  prove  to  be  the  case  ;  for  the  portability  of  aneroids,  the  facility 
with  which  they  can  be  read,  and  the  quickness  of  their  action,  would  render 
them  valuable  for  many  purposes,  if  their  indications  could  be  relied  upon. 

Eight  aneroids  were  taken.  One  of  these,  by  Casella,  marked  No.  580, 
had  been  made  for  an  earlier  journey  ;  and,  through  being  only  graduated  to 
20  inches,  was  of  no  service  for  comparison  at  great  heights.1  The  seven 
remaining  aneroids  were  constructed  expressly  for  the  expedition,  and  were 
under  trial  and  examination  for  nearly  twelve  months  before  our  departure. 
They  were  selected  from  picked  instruments,  and  only  those  were  taken 
such  as  were,  so  far  as  one  could  tell,  in  all  respects  as  perfect  as  could  be 
produced.2  These  seven  aneroids  were  marked  A  —  G-  A,  B,  and  C  were 
graduated  from  31  down  to  15  inches,  and  D,  E,  F,  G  were  graduated  from 
31  down  to  13  inches, — a  range  which  I  thought  would  be  sufficient  for  my 
purposes.3 

It  became  apparent  at  an  early  stage  of  the  journey,  a.  that  the  whole  of 
the  aneroids  had  acquired  considerable  errors  ;  &.  that  they  differed  amongst 
each  other  to  a  very  large  extent ;  and  c.  that  neither  means  of  the  whole, 
nor  means  of  those  which  held  closest  together,  nor  means  of  any  combination, 
would  give  decent  approximations  to  the  truth.  The  more  evident  this 
became  the  greater  importance  I  attached  to  the  preservation  of  the  mer- 
curials. Comparisons  of  the  aneroids  against  the  mercurials  were  neverthe- 

1  This  was  left  with  Mr.  Chambers  at  Guayaquil,  as  a  reserve  for  him,  in  case  accident 
befell  the  Standard  Mercurial ;  and  he  read  both  instruments  during  the  whole  of  our 
absence  in  the  interior. 

2  I  abstain,  however,  from  mentioning  the  names  of  the  makers  (to  whom  I  am  much 
indebted),  lest  the  remarks  which  follow  should  be  construed  to  their  disadvantage. 

3  It  proved  to  be  inadequate. 


4  COMPARISONS  IN  THE  FIELD. 

less  continued  until  the  end  of  the  journey  -1  and  after  two  months'  experience 
in  the  interior  the  behaviour  of  the  aneroids  in  ascending  and  descending 
was  so  well  ascertained  that  one  might,  I  think,  have  made  use  of  their 
indications  to  determine  differences  of  level  without  committing  very  great 
mistakes. 

.  In  the  following  pages,  I  propose  first  to  give  some  of  my  experiences, 
and  then  to  draw  such  conclusions  as  appear  to  be  warranted.2 

§  1.  Shortly  before  my  departure  from  London,  I  made  (on  October  25, 
1879)  a  final  comparison  of  the  aneroids  against  the  mercurial  barometer. 
Only  one  of  the  aneroids  corresponded  exactly,  and  of  the  others  some  were 
too  high  and  some  were  too  low,  the  greatest  difference  between  them 
amounting  to  0*225  of  an  inch,  and  the  mean  of  the  whole  showing  an  error 
of  +0-148  of  an  inch. 

§  2.  Our  ship  stopped  a  clear  day  (November  20,  1879)  at  Jamaica,  and 
I  took  the  opportunity  to  carry  the  aneroids  to  the  top  of  the  Blue  Moun- 
tains,3 comparing  them  against  the  mercurial  before  starting  and  upon  return, 
and  comparing  them  against  each  other  at  the  highest  point  attained.  The 
following  is  the  complete  record,  and  it  will  be  seen  from  it  that  the  mean 


No.  of  Barometer. 

At  start. 

At  top. 

On  return. 

Aneroid  580 

29-980 

25-430 

29-975 

A       ... 

29-850 

25-500 

29-850 

B       .      .      . 

29-800 

25-250 

29-800 

C       .      .      . 

29-700 

25-120 

29-650 

D       .      .      . 

29-850 

25-400 

29-880 

E       .      .      . 

29-800 

25-300 

29-750 

F      .     .     . 

29-750 

25-350 

29-700 

G       .      .     . 

29-800 

25-310 

29-700 

Extreme  differences 

0-280 

0-380 

0-325 

Mean  of  aneroids 

29-816 

25-332 

29-788 

Merc.  bar.  No.  554  . 

29-876 

. 

29-854 

Mean  error  of  aneroids 

-0-060 

-0-066 

error  of  the  aneroids  (which  in  London  was  +  0-148)  had  changed  on  arrival 
at  Kingston  to  -  0*060,  and  upon  return  in  the  evening  of  November  20 
it  was  still  further  increased  to  —0-066. 

1  In  all  the  comparisons  which  are  made  throughout  this  paper  the  readings  of  the 
mercurial  barometer  are  reduced  to  32°  Faht. 

2  Paragraphs  1-10  should  be  read  in  connection  with  the  tables  at  pp.  10,  11. 

3  Drove  to  Gordonstown,  walked  thence  to  Newcastle,  and  on  until  we  came  to  a 
notch  in  the  mountains  commanding  a  view  of  the  northern  side  of  the  island.     Read  the 
aneroids  at  this  place. 


COMPARISONS  IN  THE  FIELD. 


§  3.  Comparisons  were  again  made  at  Colon  and  Guayaquil,1  and  at 
neither  of  these  places  (at  the  level  of  the  sea)  was  there  any  further  in- 
crease in  the  mean  error  of  the  aneroids  ;  but  at  Munapamba  (where  we 
commenced  to  mount  the  outer  Andean  ranges)  their  difference  amongst  each 
other  had  risen  to  0*500  of  an  inch,  and  the  mean  error  was  increased  to 
-0-098  of  an  inch. 

§  4.  At  Tambo  Gobierno  (the  culminating  point  of  the  road  over  the 
outer  Andean  range),  10,417  feet  above  the  sea,  the  mean  error  of  the 
aneroids  had  risen  to  —  0*487  of  an  inch,  and  the  extreme  difference  of  their 
readings  amounted  to  0*715. 

§  5.  With  the  descent  on  the  other  side  the  aneroids  came  more  closely 
together,  but  their  mean  error  continued  to  augment, — being  upon  arrival 
at  Guaranda2  (8894  feet)  -0*520,  and  it  rose  in  one  week  to  —0*655. 
The  '  greatest  difference '  also  continued  to  increase,  and  it  stood  on  Christmas 
Day  at  0*800  of  an  inch.  The  following  record,  showing  the  continual 
increases  in  the  errors,  will  be  found  interesting. 


No.  of  Barometer. 

Dec.  18,  1879. 

Dec.  20,  1879. 

Dec.  23,  1879. 

Dec.  25,  1879. 

Aneroid  A      .... 

21*700 

21*700 

21-700 

21*600 

„        B      .      .      .      . 

21*170 

20*960 

20*940 

20*870 

„       D      .      .      .      . 

21*460 

21*430 

21-450 

21*390 

„       E      .      .      .      . 

21*500 

21*500 

21*500 

21*440 

»       F      .      .      .      . 

21*220 

21*030 

20*950 

20-800 

„       G      .      .      .      . 

21*400 

21-380 

21*300 

21*300 

Extreme  differences 

0*530 

0*740 

0*760 

0*800 

Mean  of  aneroids     .     . 

21*408 

21-333 

21*321 

21-233 

Mean  Merc.  bar.       .     . 

21*928 

21*912 

21*934 

21*888 

Mean  errors  of  aneroids 

-0*520 

-0*579 

-0*613 

-0*655 

§  6.  Upon  December  26,  1879,  we  encamped  on  the  Arenal  (14,375 
feet),  at  the  foot  of  Chimborazo,  and  011  the  morning  of  the  27th  the  mean 
error  of  the  aneroids  was  found  to  be  -  0*737,  and  their  greatest  difference 
0-880. 

§  7.  We  then  moved  up  to  the  Second  Camp  on  Chimborazo  (16,664 
feet),  the  mean  error  continuing  to  rise,  and  amounting  upon  December  30 
to  -0*903. 

§  8.  Upon  arrival  at  the  Third  Camp  (17,285  feet)  I  found  that  com- 
parisons at  greater  heights  would  have  to  be  made  between  five  aneroids 

1  As  aneroid  580  was  left  at  Guayaquil,  the  comparisons  are  now  between  the  seven 
remaining  instruments. 

2  Aneroid  C  was  lost  or  stolen  shortly  before  arrival  at  Guaranda,  thus  reducing  the 
number  under  comparison  to  six. 


6 


COMPARISONS  IN  THE  FIELD. 


only,  as  the  error  which  B  had  acquired  was  so  large  that  we  had  already 
got  beyond  its  range.  The  mean  error  of  the  aneroids  at  this  point  amounted 
to  -0-974,  and  their  greatest  difference  to  1-120  inches. 

§  9.  The  aneroids  D  and  E  were  alone  taken  to  the  summit  of  Chim- 
borazo  on  the  first  ascent,  January  4,  1880,  and  these  two  were  taken 
because  they  were  working  better  than  the  others.  The  readings  on  the 
summit  are  instructive. 


Merc.  bar.  No.  558  . 
Aneroid  D 
do.      E 


14-110  inches. 

13-050       „ 

12-900  (by  estimation). 


The  mean  of  the  two  aneroids  is  seen  to  be  12-975  inches,  and  the 
error  of  this  upon  the  mercurial  —1-135  inches.  I  defer  comment  to  a 
later  point. 

§  10.  Their  prolonged  residence  upon  Chimborazo  seriously  affected  the 
constitutions  of  aneroids  F  and  G.  The  index  of  the  latter  instrument 
became  immovable,  and  the  former  was  afflicted  with  a  quivering  action 
which  set  observation  at  defiance.  Comparisons  for  the  remainder  of  the 
journey  were  thus  restricted  to  A,  B,  D,  E  only,  and  they  are  given  in  the 
tables  upon  pp.  10,  11  so  far  as  is  necessary  to  support  the  statements, —  a. 
that  the  aneroids  acquired  considerable  errors  ;  b.  that  they  differed  amongst 
each  other  to  a  very  large  extent ;  and  c.  that  their  means  were  far  from  the 
truth. 

§  11.  After  we  had  been  three  to  four  weeks  in  the  interior,  the  aneroids 
A,  B,  D,  E  were  found  to  hold  pretty  constantly  together  (or,  speaking  more 
correctly,  their  movements  were  harmonious),  and  they  seemed  to  have 
acquired  their  maximum  errors  for  the  pressures  at  which  they  were  used.1 
Of  the  above  four  instruments  B  had  the  largest  index-error,  and  the  following 
table  shows  that  it  remained  tolerably  constant.  It  then  became  interesting 


Date. 

Place  of  observation. 

Merc.  bar.  558. 

Aneroid  B. 

Error  of  B. 

Jan.  14,  1880 

Chuquipoquio 

19  -683  inch 

17-820  inch 

-  1-863  inch 

Feb.    8,      „ 

Hac.  cle  la  Rosario 

20-805    „ 

19-100    „ 

-1-705    „ 

)      » 

Illiniza  (S.  side)  . 

17-239    „ 

15-400    „ 

-1-839    „ 

„     16,      „ 

On  Cotopaxi   .     . 

17-431     „ 

15-650    „ 

-1-781    „ 

„     26,     „ 

Machachi   .     .     . 

21-142    „ 

19-360    „ 

-1-782    „ 

Mar.  28,     „ 

Hac.  Guachala     . 

21-618    „ 

19-950    „ 

-1-668    „ 

May  1  5,     „ 

Quito     .... 

21-631     ., 

19-990    „ 

-1-641    „ 

June  8,      „ 

Illiniza  (N.  side)  . 

17-222    „ 

15-400    „ 

-1-822    „ 

to  observe  whether  aneroids  which  had  acquired   such  large  index-errors 
could  be  usefully  employed  for  the  determination  of  differences  of  level. 

1  See  the  last  column  of  the  table  at  p.  11. 


COMPARISONS  IN  THE  FIELD.  7 

§  12.  Upon  the  journey  to  the  north  of  Quito  I  carried  mere.  bar.  No. 
558  and  aneroids  A  and  B,  and  upon  arrival  at  the  top  of  the  great  ravine 
of  Guallabamba  took  simultaneous  observations  of  the  mercurial  and  the 
aneroids.  At  the  bottom  of  the  ravine,  two  hours  and  a  half  later,  readings 
of  all  three  were  repeated  with  the  following  result : — 

Date.  Barometer.  Read  at  top.  Read  at  bottom. 

Mar.  27,  1880  Merc.  bar.  558  (red.  to  32°  Faht.)  21-692          23-929 

do.  Aneroid  A  21-140          23-400 

do.  do.       B  19-940          22-200 

The  rise  of  the  Mercurial  Barometer  was  2*237  inches, 
do.         do.     Aneroid  A  ,,2-260       „ 

do.         do.  „        B  „    2-260       „ 

§  13.  The  foregoing  experiment  is  a  descending  one  employing  two  ane- 
roids, and  the  next  is  an  ascending  one  in  which  three  were  observed.  Upon 
the  occasion  of  the  attempt  to  ascend  Illiniza  from  the  north,  I  read  the 
three  aneroids  A,  B,  D  before  departure  from  Machachi  (9839  feet),  and  did 
the  same  at  our  camp  (15,446  feet). 

Date. 

June  8,  1880 
do. 
do. 
do. 

The  fall  of  the  Mercurial  Barometer  was  3*954  inches. 
The  mean  fall  of  the  three  aneroids  was  3*960       „ 

§  14.  Upon  the  second  ascent  of  Chimborazo  I  carried  aneroids  A  and  E 
to  the  summit,  reading  them  at  the  fifth  camp  and  at  the  top.  Aneroid  A 
became  much  out  of  range,  and  I  therefore  cannot  give  its  reading. 

Date.  Barometer.  Fifth  Camp  (4  a.m.)  Summit  (2  p.m.) 

July  3,  1880          Merc.  bar.  558          16-931  inches          14-044  inches, 
do.  Aneroid  E  16*060     „  12*990     „ 

The  fall  of  the  Mercurial  Barometer  was  2*887  inches, 
do.  Aneroid  E  „    3*070     „ 

§  15.  The  examples  which  are  quoted  in  §§  12,  13,  14  give  the  closest 
coincidences  that  I  can  mention  from  amongst  experiments  of  this  order. 
Upon  the  whole,  it  appeared  to  me  that  better  values  could  be  obtained 
from  aneroids  by  taking  the  mean  of  ascending  and  descending  observations,1 
than  by  taking  the  means  of  either  ascending  or  descending  ones  alone,  and 
I  now  give  an  example  in  which  this  method  of  treatment  was  adopted. 

On  March  19,  1880,  I  carried  the  aneroids  A,  B,  D,  E  from  our  lodging 

1  When  ascent  and  descent  are  only  a  short  space  of  time  apart. 


Barometer. 
Merc.  bar.  558 
Aneroid  A 
do.      B 
do.      D 

At  Machachi  (9  a.m.) 
21-176  inches 
20-650     „ 
19-530     „ 
20-290     „ 

At  Camp  (6  p.m.) 
17*222  inches. 
16*810     „ 
15-400     „ 
16-380     „ 

8 


COMPARISONS  IN  THE  FIELD. 


at  Quito  to  the  top  of  the  hill  called  the  Panecillo,  on  this  occasion  reading 
the  'scales  of  feet'  upon  them  before  departure,  and  again  upon  return  to 
Quito.  From  the  means  of  the  ascending  and  descending  readings,  the 
summit  of  the  Panecillo  appears  to  be  651*25  feet  above  the  level  of  the 
principal  Plaza  of  Quito,  which  from  the  mean  of  twenty-two  observations  of 
mercurial  barometer  by  myself  is  found  to  be  9343 '3  feet  above  the  sea.  I 
have  no  observation  of  mercurial  barometer  on  the  Panecillo  ;  and,  if  I  had, 
should  still  quote  by  preference  the  independent  observations  of  Messrs. 
Reiss  and  Stiibel,  who,  from  the  mean  of  a  large  number  of  observations  of 
mercurial  barometer,  give  for  the  height  of  Quito  9350  feet,  and  for  the 
Panecillo  (two  observations  of  m.b.)  10,007  feet.  Their  difference  of  level 
therefore  is  657  feet,  or  5  feet  9  inches  more  than  the  height  indicated  by 
the  aneroids. 


Barometer. 

At  Quito,  in 
Hotel. 

Summit  of 
Panecillo. 

—  a  rise  of 

On  return 
to  Quito. 

=  a  fall  of 

Aneroid  A 

10,680  feet 

11,325  feet 

645  feet 

10,760  feet 

565  feet 

do.       B 

12,310    „ 

13,050    „ 

740     „ 

12,390    „ 

660     „ 

do.      D 

11,260    „ 

11,950    „ 

690     „ 

11,340     „ 

610     „ 

do.      E 

11,000     „ 

11,680    „ 

680     „ 

11,060     „ 

620     „ 

Mean  of  ascending  readings  688*75  feet. 
Mean  of  descending  do.  613 '75  feet. 
Mean  of  ascending  and  descending  651-25  feet. 

§  16.  As  the  journey  approached  its  termination,  I  became  curious  to 
observe  how  the  aneroids  would  read  against  the  mercurials  upon  return 
to  the  level  of  the  sea.  We  arrived  at  Guayaquil  again  on  July  13,  1880, 
and  the  barometers  were  compared  against  each  other  from  the  16th  to  the 
27th.1  The  error  of  aneroid  A  upon  the  16th  was  -  0-361  of  an  inch,  and 
of  E  -  0-321,  but  by  the  27th  their  respective  errors  diminished  to  -  0-341 
and  -  0-291.  I  have  not  allowed  the  index  of  either  to  be  altered.  They 
continued  to  recover  in  the  course  of  time  ;  and  I  found,  upon  January  9, 
1885,  that  aneroid  E  possessed  an  index-error  of  +0*160,  which  was  very 
nearly  its  error  upon  the  last  comparison  in  1879  before  our  start,  when 
it  was  seen  to  be  +0*182.  Aneroid  A  did  not  recover  with  the  same 
rapidity.  Upon  January  9,  1885,  its  error  had  diminished  to  —0*200,  and 
in  five  years  more  it  recovered  another  tenth  of  an  inch, 

§  1 7.  In  the  tables  at  pp.  1 2,  1 3  the  comparisons  of  the  aneroids  A  and  E 
are  presented  separated  from  the  others.  These  two  instruments  were  those 
which  were  most  consistent  in  their  behaviour,  and  were  those  which  were 
most  frequently  employed.  From  inspection  of  the  tables  it  will  be  immedi- 
ately apparent  that  '  a  good  return '  is  of  little  value  as  a  test  of  working. 

1  See  the  tables  at  pp.  12,  13  for  this  and  for  the  succeeding  paragraph. 


COMPARISONS  IN  THE  FIELD.  9 

Upon  the  last  comparison  before  departure,  these  two  aneroids  possessed  almost 
exactly  similar  index-errors  ( +  0  •  1 7  2  and  +  0  •  1 8  2),  and  upon  return  to  Guaya- 
quil their  index-errors  were  not  far  apart  (  -  0-341  and  —  0-291).  It  would 
have  appeared  legitimate  to  conclude  that  their  working  had  closely  corre- 
sponded, but  inspection  of  the  last  two  columns  of  the  table  shows  that  such 
a  conclusion  would  have  been  extremely  erroneous.  The  case  of  E,  taken  by 
itself,  is  still  stronger.  This,  in  course  of  time,  '  returned '  almost  perfectly  ; 
and  inasmuch  as  this  instrument  (like  all  the  others)  was  tested  before  de- 
parture, inch  by  inch,  against  the  mercurial  barometer  under  the  air-pump, 
and  corresponded  almost  perfectly,  it  would  have  seemed  right  to  conclude 
that  its  readings  in  the  interim  must  have  been  nearly  free  from  error.  Yet 
this  instrument,  at  the  greatest  height  at  which  it  was  compared,  was  found 
to  possess  a  minus  error  of  an  inch  and  a  fifth,  the  value  of  which,  at  the 
elevation  in  question,  exceeds  two  thousand  feet  (see  §  9). 

§  18.  Some  of  the  more  important  conclusions  which  must  be  arrived 
at  from  consideration  of  the  results  of  these  comparisons  of  the  aneroid 
against  the  mercurial  barometer  are  so  obvious  that  I  consider  it  unnecessary 
even  to  point  them  out ;  and,  in  the  remarks  which  follow,  I  endeavour 
more  to  indicate  the  ways  in  which  the  aneroid  may  be  advantageously 
used,  than  to  emphasize  the  objections  which  might  be  urged  against  its 
employment. 

A.  It  seems  possible,  without  reference  to  a  standard,  by  intercomparison 
of  a  number  of  aneroids,  to  discriminate  between  them,  and  to  select  those 
in  which  most  confidence  should  be  placed. 

B.  That,  with  aneroids  of  the  present  construction,  it  is  unlikely  that 
decent  approximations  to  the  truth  will  be  obtained  at  low  pressures,  even 
when  employing  a  large  number  of  instruments.      The  errors  of  the  whole 
series  (A  -  G)  were  invariably  minus  ones,  and  in  the  worst  cases  amounted 
to  as  much  as  two  inches  upon  the  mercurial  barometer. 

C.  That  differences  of  level  at  great  heights  (low  pressures)  may  be 
determined  with  considerable  accuracy  with  aneroids,  even  when  they  have 
acquired  very  large  index-errors. 

D.  That  in  observations  of  this  description  a  nearer  approach  to  the 
truth  is  generally  obtained  by  employing  the  mean  of  ascending  and  descend- 
ing readings  than  by  taking  ascending  or  descending  readings  separately. 

E.  That  the  test  which  is   commonly  applied  of  comparing  for  brief 
periods  (minutes  or  hours)  aneroids  against  mercurial  barometers  under  the 
air-pump  is  of  little  or  no  value  in  determining  the  errors  which  will  appear 
in  aneroids  used  at  low  pressures  for  long  periods  (weeks  or  months). 

F.  That,  similarly,  comparisons  of  aneroids  against  mercurial  barometers 
in  balloon  for  a  brief  space  of  time  afford  little  or  no  clue  to  the  errors 
which  will  be  exhibited  by  the  former  when  subjected  to  low  pressures  for 

C 


10 


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14  COMPARISONS  IN  THE  FIELD. 

prolonged  periods.  [The  balloon  test  is  only  a  repetition  of  the  air-pump 
test.  In  the  former  case  the  instruments  are  exposed  to  a  natural,  and  in 
the  latter  case  to  an  artificial  diminution  of  pressure  ;  and  if  the  duration  of 
time  is  equal  in  each  case  the  results  ought  to  correspond  exactly.] 

G.  That  very  material  errors  may  be  fallen  into  by  regarding  'a  good 
return '  at  the  level  of  the  sea  as  a  proof  of  correct  working,  at  low  pressures, 
of  aneroids  of  the  present  construction. 

H.  That  for  the  detection  of  such  errors  as  aneroids  (of  the  present  con- 
struction) will  exhibit  when  subjected  to  low  pressures  for  a  length  of  time, 
aneroids  should  be  subjected  artificially  to  similar  pressures  for  a  long 
period. 


PART  2.-EXPERIMENTS  IN  THE  WORKSHOP. 


Throughout  the  second  part  of  this  paper,  as  in  the  first  part,  my  remarks 
are  principally  confined  to  comparisons  of  the  aneroid  against  the  mercurial 
barometer.  I  enter  only  incidentally  into  consideration  of  uses  to  which  these 
instruments  can  be  put,  and  do  not  attempt  to  explain  the  mechanical  im- 
perfections that  cause  the  errors  to  which  reference  is  made.  The  question 
which  I  attempt  to  answer  is,  Do  aneroids,  under  ordinary  conditions,  read 
truly  against  the  mercurial  barometer  ? 

The  earliest  experiments  which  were  made  in  the  workshop  were  under- 
taken with  the  view  of  confirming  or  upsetting  the  conclusions  which  were 
arrived  at  from  observation  in  the  field  (§  18),  and  they  were  directed  first 
of  all  to  learn  whether  it  is  a  fact  that  all  aneroids  lose  upon  the  mercurial 
barometer  *  if  submitted  to  diminished  pressure  for  a  length  of  time ;  to 
observe  the  length  of  time  during  which  the  loss  continues  to  augment,  and 
to  ascertain  the  extent  of  the  loss  that  occurs. 

These  earliest  experiments  were  made  entirely  with  aneroids  of  Mr.  J.  J. 
Hicks'  manufacture,  and  they  confirmed  the  observations  made  in  the  field. 
I  felt,  however,  that  it  was  desirable  to  include  instruments  by  other  makers, 
and  I  continued  to  experiment  until  70  aneroids  had  been  submitted  to  ex- 
amination, and  could  be  reported  upon.2 

Every  aneroid  which  was  tested,  without  exception,  lost  upon  the  mer- 
curial barometer  when  submitted  to  diminished  pressure  for  a  length  of  time 
— that  is  to  say,  for  a  day,  a  week,  a  month  and  upwards.  It  was  found 
that  the  greater  part  of  such  loss  as  occurred  took  place  during  the  first  week. 
The  experiments  were  then  continued  to  endeavour  to  learn  what  proportion 
of  the  loss  which  occurred  during  the  first  week  took  place  during  the  first 
day. 

When  this  class  of  experiment  had  been  continued  for  many  months,  I 
turned  my  attention  to  the  behaviour  of  aneroids  upon  their  being  allowed 
to  return  to  normal  pressure  after  they  had  experienced  diminished  pressure 
for  a  length  of  time.  It  was  found  that  they  always  recovered  a  large  part 
of  their  loss,  and  sometimes  gained  more  than  they  had  previously  lost.  It 
was  found  that  the  recovery  might  extend  over  several  weeks,  and  that  the 
greater  part  of  the  recovery  or  gain  usually  occurred  in  the  first  week.  As 
the  amount  which  was  recovered  very  seldom  exactly  equalled  the  amount 
of  the  previous  loss,  in  the  great  majority  of  cases  there  was  a  marked  change 
in  the  index-errors,  and,  in  some  instances,  a  large  alteration. 

1  See  §  21  for  explanation  of  the  expression  "loss  upon  the  mercurial  barometer.'' 

2  A  number  of  others  were  tested.     Some  behaved  well,  but  they  are  not  included 
here,  as  they  did  not  bear  makers'  names. 


16  EXPERIMENTS  IN  THE   WORKSHOP. 

I  then  endeavoured  to  learn  whether  aneroids  which  possessed  large 
index-errors  could  nevertheless  be  usefully  employed  for  the  measurement  of 
variations  of  pressure,  and  found  that  in  the  majority  of  cases  they  might  be 
so  employed.  Other  experiments  having  a  practical  bearing  suggested  them- 
selves from  time  to  time. 

§  19.  The  method  by  which  the  aneroids  were  tested  in  these  experi- 
ments was  that  which  is  habitually  employed  during  *  verification '  of  these 
instruments.  The  aneroids  were  placed  under  the  receiver  of  an  air-pump, 
to  which  there  was  an  attached  mercurial  barometer.  Upon  air  being  with- 
drawn, there  was  simultaneous  reduction  in  pressure  both  for  the  aneroids 
and  for  the  mercurial  The  indications  of  the  latter  were  frequently  checked 
by  reference  to  a  standard  mercurial  barometer,  hanging  alongside. 

§  20.  Although  my  method  of  testing  was  the  same  as  that  employed 
during  '  verification,'  there  was  one  essential  point  of  difference  between  the 
verification  tests  and  my  own,  namely  in  the  length  of  time  during  which 
the  aneroids  were  kept  at  reduced  pressures.  I  have  good  authority  for  say- 
ing that  even  when  an  aneroid  is  verified  at  Kew  Observatory  inch  by  inch, 
down  to  as  low  as  15  inches,  it  is  unusual  to.  occupy  more  than  an  hour  in 
the  operation, — about  one-half  of  which  amount  of  time  will  be  consumed 
whilst  pressure  is  being  reduced,  and  the  rest  while  pressure  is  being  restored. 

This,  also,  is  about  the  length  of  time  ordinarily  occupied  during  the 
manufacture  of  aneroids  upon  the  process  termed  'pointing,5  i.e.  laying  off 
the  scale  on  the  dial  of  an  aneroid  (by  comparison  with  an  attached  mercurial 
barometer)  prior  to  graduation.  Therefore,  what  verification  amounts  to  is 
this.  It  is  a  repetition  of  the  temporary  reduction  of  pressure  to  which 
aneroids  have  been  subjected  in  the  course  of  manufacture  ;  and  one  learns 
from  verification  whether  the  '  pointing '  and  the  subsequent  graduation  have 
been  accurately  performed.  One  does  not  learn  from  it  the  errors  that 
will  be  manifested  by  aneroids  which  may  be  subjected  to  a  reduction  of 
pressure  for  a  greater  length  of  time.  In  order  that  my  tests  in  the  workshop 
might  be  the  equivalent  of  the  tests  to  which  aneroids  are  put  in  the  field  I 
kept  the  instruments  at  various  pressures  between  26  and  14  inches  for 
periods  of  days,  weeks,  and  even  months  at  a  time. 

§  21.  The  first  six  aneroids  that  were  experimented  upon  were  taken 
from  the  stock  of  Mr.  Hicks,  and  were  marked  temporarily  1-6.  These  were 
placed  under  the  receiver,  and  had  pressure  reduced  to  22*5  inches,  and 
were  kept  continuously  at  that  pressure  for  six  weeks.  The  annexed  table 
scarcely  requires  explanation.  In  Column  1  the  errors  of  the  aneroids  are  given 
which  were  exhibited  upon  their  being  reduced  to  22 -5  inches.  In  Columns 
2-7  the  errors  are  given  which  they  showed  at  the  end  of  each  week,  during 
six  successive  weeks ;  and  in  Column  8  the  total  amount  of  the  loss  is  stated 
that  occurred  during  the  six  weeks.  In  the  case  of  aneroid  No.  1,  a  + 
error  of  0-159  was  converted  into  a  -  error  of  0-335.  The  actual  loss 
amounted  therefore  to  0-494  of  an  inch.  In  the  case  of  No.  5,  the  —  error 
of  0-016  was  increased  to  -0-485.  The  actual  loss  was  therefore  0-469  of 
an  inch.  The  amounts  so  lost  I  term  "  loss  upon  the  mercurial  barometer." 


EXPERIMENTS  IN  THE  WORKSHOP. 


18 


EXPERIMENTS  IN  THE  WORKSHOP. 


Several  points  came  out  very  clearly  during  this  experiment  The  first 
and  principal  one  was  that  the  whole  six  instruments  lost  considerably  upon 
the  mercurial  barometer.  Another,  and  it  seemed  to  me  an  important  one, 
was  that  the  greater  part  of  the  loss  occurred  in  each  instance  during  the  first 
week  In  every  succeeding  experiment  these  facts  were  confirmed.  Another 
point  was  the  large  difference  in  the  loss  in  the  different  instruments — the 
least  being  0-209  and  the  greatest  0*494  of  an  inch.  The  gradual  stoppage 
in  increase  of  the  loss  is  best  seen  by  examining  the  line  in  which  the  mean 
errors  of  the  whole  are  given.  At  the  end  of  the  fifth  week  there  was  no 
perceptible  increase  in  the  mean  error,  but  at  the  end  of  the  sixth  week  a 
slight  increase  appeared.  This  was  due  to  Nos.  3  and  5,  which  probably 
would  have  continued  to  lose  some  small  amounts  for  several  weeks  longer. 

§  22.  The  emphatic  manner  in  which  this  first  experiment  in  the  work- 
shop confirmed  the  experiences  in  the  field  keenly  interested  those  with 
whom  I  was  associated,  and  immediately  upon  its  termination  we  started  a 
fresh  series  of  aneroids  (marked  temporarily  10-12)  at  a  pressure  of  17  inches, 
and  kept  them  at  that  pressure  during  five  weeks,  with  the  following  results. 

EXPERIMENT  IN  WHICH  THREE  ANEROIDS  (No.  10,  WATCH-SIZE  ;  Nos.  11,  12, 

THREE    INCHES    DIAMETER)    WERE    KEPT    AT    A    PRESSURE    OF 
17    INCHES    FOR    FIVE    WEEKS. 


Aneroid. 

1. 

Errors 
of  aneroids 
at  17  inches 
at  start  of  the 
experiment. 

2. 

Errors 
of  aneroids 
at  the  end  of 
the  first  week. 

3. 

Errors 
of  aneroids 
at  the  end  of 
the  fifth  week. 

4. 

Loss  of 
aneroids  upon 
the  Merc.  Bar. 
in  five  weeks. 

inch. 

inch. 

inch. 

inch. 

No.  10  (Hicks). 

-0-023 

-0-731 

-0-944 

0-921 

,,    11       ,»        • 

-0-203 

-0-721 

-0-909 

0-706 

„    12      „        • 

-0-043 

-0-531 

-0-709 

0-666 

Mean  errors  of  aneroids  ^ 
on    Mercurial    Baro-  1 
meter  (reduced  to  32°  f 
Faht.)                          ) 

-0-090 

-0-661 

-0-854 

0-764 

Note.  In  calculations  for  altitude,  the  value  of  0'764  of  an  inch,  at  a  pressure 
of  17  inches,  is  about  1220  feet. 

I  do  not  feel  it  necessary  to  give  this  second  experiment  in  as  full  detail 
as  the  previous  one.  Each  aneroid  lost  considerably  upon  the  mercurial 
barometer  ;  in  each  case  the  greater  part  of  the  loss  occurred  in  the  first 
week  ;  the  loss  was  different  in  each  instrument ;  and  the  loss  seemed  to 
cease  to  augment  about  the  fourth  or  fifth  week.  No.  10  lost  nearly  an  inch 
(0-921),  and  the  mean  loss  of  the  three  instruments  amounted  to  0-764  of  an 
inch. 


EXPERIMENTS  IN  THE   WORKSHOP. 


19 


§  23.  When  this  experiment  was  concluded  I  started  a  third  series  of 
aneroids  (Nos.  7,  8,  9),  three  inches  diameter  each,  at  a  pressure  of  1 6  inches, 
and  kept  them  at  that  pressure  for  two  months.  This  series  lost  less  at 
16  inches  during 'six  weeks  than  Nos.  10,  11,  and  12  had  lost  at  17  inches 
during  five  weeks.  But  the  loss,  as  before,  was  considerable  in  each  instru- 
ment ;  the  greater  part  of  the  loss  occurred  during  the  first  week  ;  and  the 
loss  was  comparatively  trifling  after  the  fourth  week. 

EXPERIMENT  IN  WHICH  THREE  ANEROIDS  (EACH  THREE  INCHES  DIAMETER) 

WERE    KEPT    AT    A    PRESSURE    OF    16    INCHES    DURING    EIGHT    WEEKS. 


Aneroid. 

1. 

Errors 
of  aneroids 
at  16  inches 
at  start  of  the 
experiment. 

2. 

Errors 
of  aneroids 
at  the  end  of 
the  first  week. 

3. 

Errors 
of  aneroids  at 
the  end  of  the 
second  week. 

4. 

Errors 
of  aneroids 
at  the  end  of 
the  third  week. 

inch. 

inch. 

inch. 

inch. 

No.  7  (Hicks) 

+  0-104 

-0-118 

-0-180 

-0-206 

55        &               55 

+  0-069 

-0-223 

-0-305 

-0-306 

„    9        „      . 

+  0-014 

-0-368 

-0-405 

-0-451 

Mean  errors  of  ane-^ 
roids  on  Mercurial  I 
Barometer  (reduced  f 
to  32°  Faht.)            J 

+  0-062 

-0-236 

-0-297 

-0-321 

5. 

6. 

7. 

8. 

9. 

10. 

Errors 
of  aneroids 
at  the  end  of 
jhe  fourth  week. 

Errors 
of  aneroids 
at  the  end  of 
the  fifth  week. 

Errors 
of  aneroids 
at  the  end  of 
the  sixth  week. 

Errors 
of  aneroids  at 
the  end  of  the 
seventh  week. 

Errors 
of  aneroids 
at  the  end  of 
the  eighth  week. 

Loss  of 
aneroids  upon 
the  Merc.  Bar. 
in  eight  weeks. 

inch. 

inch. 

inch. 

inch. 

inch. 

inch. 

-0-252 

-0-276 

-0-285 

-0-306 

-0-271 

0-375 

-0-322 

-0-326 

-0-355 

-0-331 

-0-336 

0-405 

-0-472 

-0-476 

-0-495 

-0-506 

-0-531 

0-545 

-0-349 

-0-359 

-0-378 

-0-381 

-0-379 

0-442 

Note.  In  calculations  for  altitude,  the  value  of  0'442  of  an  inch,  at  a  pressure 
of  16  inches,  is  about  750  feet. 

§  24.  After  this  experiment,  I  proceeded  to  test  four  aneroids  which  had 
been  specially  made,  and  embraced  some  peculiarities  in  construction.  In 
this  (the  fourth)  series  each  instrument  lost  considerably  upon  the  mercurial 


20 


EXPERIMENTS  IN  THE  WORKSHOP. 


barometer  ;  the  greater  part  of  the  loss  occurred  during  the  first  week  ;  and 
the  mean  error  of  the  whole  four  ceased  to  augment  after  the  fourth  week. 

EXPERIMENT  IN  WHICH  FOUR  ANEROIDS  (EACH  FOUR  AND  A  HALF  INCHES 

DIAMETER)  WERE  KEPT  AT  A  PRESSURE  OF  19  INCHES  DURING 

FIVE  WEEKS. 


Aneroids  13,  14,  15,  16 
(Hicks). 

Mean  error  of 
the  aneroids 
at  19  inches 
at  start  of  the 
experiment. 

Mean  error  of 
the  aneroids 
at  the  end  of 
the  first  week. 

Mean  error  of 
the  aneroids 
at  the  end  of 
the  fifth  week. 

Mean  loss 
upon  Mercurial 
Barometer  in 
five  weeks. 

inch. 

inch. 

inch. 

inch. 

Mean  errors  of  the  ftnir^j 

aneroids  on  the  Mer-  1 
curial  Barometer  (re-  | 
ducedto32°Faht.)    J 

+  0-013 

-0-246 

-0-348 

0-361 

Note.  In  calculations  for  altitude,  the  value  of  0'361  of  an  inch,  at  a  pressure 
of  19  inches,  is  about  520  feet. 

§  25.  These  four  experiments  (as  well  as  subsequent  ones)  showed  clearly 
that  the  greater  part  of  the  loss  which  occurred  took  place  during  the  first 
week.  From  the  following  table  it  will  be  seen  that  in  every  series  the 
mean  loss  in  a  week  exceeded  two-thirds  of  the  total  mean  loss  upon  the 
mercurial  barometer. 


Number  of 
Aneroids 
employed. 

Pressures  at 
which  they 
were  kept. 

Length  of  time 
during  which 
they  were 
kept  at  these 
pressures. 

Mean  loss  of 
each  series  upon 
the  Merc.  Bar. 
in  one  week. 

Total  mean  loss 
of  each  series 
upon  the 
Mercurial  Baro- 
meter. 

inches. 

inch. 

inch. 

6 

22-5 

6  weeks 

0-298 

0-373 

3 

17 

5     „ 

0-571 

0-764 

3 

16 

8     „ 

0-298 

0-442 

4 

19 

5      „ 

0-259 

0-361 

§  26.  As  it  appeared  from  these  experiments  that  the  greater  (and  more 
important)  part  of  the  loss  which  occurred  took  place  in  the  first  week,  I  con- 
tinued by  testing  aneroids,  for  one  week  each,  at  every  inch  of  the  barometer 
between  14  and  26  inches,  and  endeavoured  to  procure  instruments  by  a 
diversity  of  makers  and  of  various  diameters.  This  series  of  experiments 
necessarily  extended  over  several  years,  as  it  was  seldom  possible  to  test  more 
than  a  few  instruments  at  a  time,  owing  to  difficulty  in  obtaining  at  any  one 
time  a  number  of  instruments  with  similar  ranges.  It  included  aneroids  by 
Hicks,  Casella,  Adie,  Elliott,  Negretti  and  Zambra,  Cooke  and  Sons,  Secretan, 
and  Hilger. 


EXPERIMENTS  IN  THE   WORKSHOP. 


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HI 


EXPERIMENTS  IN  THE  WORKSHOP.  25 

These  tables  speak  for  themselves.  I  draw  attention,  however,  to  the 
last  column  of  each,  in  which  there  is  shown  approximately  the  errors  in 
determinations  of  altitude  which  would  have  been  probable  if  these  particular 
aneroids  had  been  employed  in  the  field,  at  the  mentioned  pressures,  for  one 
week  ;  and  I  point  out  especially  that  these  errors,  serious  as  they  are,  are 
(taking  them  as  a  whole)  probably  only  about  two-thirds  of  the  maximum  errors 
which  these  particular  aneroids  would  have  developed,  if  they  had  been  kept 
continuously  at  the  mentioned  pressures  for  one  month  and  upwards. 

§  27.  It  appears  to  me  to  follow,  and  to  be  indubitable,  that  a  great  part 
of  the  altitudes  throughout  the  world  which  depend  upon  observations  of 
aneroid  barometers  made  while  ascending  must  be  too  high,  and  that  a  general 
lowering  of  them  will  be  found  necessary  ;  and  that  it  is  probable  the  reduc- 
tion in  height  will  have  to  be  at  a  greater  rate  per  cent  in  the  case  of  the 
loftier  positions  than  in  the  case  of  the  inferior  ones,  and  with  those  which 
are  in  the  interiors  of  continents  than  with  those  in  the  neighbourhood  of 
the  sea-level. 

§  28.  Concurrently  with  these  observations  to  attempt  to  learn  the 
extent  of  the  loss  of  aneroids  upon  the  mercurial  barometer  on  being  sub- 
mitted to  diminished  pressures  for  a  week,  I  observed  the  loss  which  occurred 
in  the  first  day  of  the  first  week.  This  is  variable, — sometimes  being  about 
one-third  of  the  week's  loss,1  and  sometimes  more  than  three-fourths  of  it.  This 
is  illustrated  by  the  examples  which  are  given  on  p.  26. 

§  29.  The  experiments  which  have  been  already  quoted  indicate  that  the 
loss  in  aneroids  upon  the  mercurial  barometer  augments  at  a  constantly 
diminishing  rate,  provided  they  are  kept  continuously  at  the  same  pressure. 
The  loss  is  greater  in  the  first  week  than  it  is  in  the  second,  or  in  any  suc- 
ceeding week.  It  is  rare,  however,  to  observe  in  any  seven  successive  days 
a  perfectly  regular  (or  symmetrical)  increase  in  the  errors.  Minor  imper- 
fections of  construction  prevent  perfectly  harmonious  readings,  and  render 
it  impossible  to  say  more  than  that  the  loss  during  the  first  day  of  the 
first  week  (so  far  as  my  observation  extends)  is  almost  always  greater  than 
during  any  subsequent  one  in  the  first  week.  A  few  examples  are  given 
upon  p.  27  in  illustration. 

§  30.  The  loss  in  aneroids  upon  the  mercurial  barometer  can  be  observed 
in  almost  all  instruments  during  the  first  hour  they  are  subjected  to  dimin- 
ished pressure,  if  the  diminution  in  pressure  amounts  to  several  inches  ;  and 
in  aneroids  giving  the  inch  of  the  mercurial  barometer  that  length  upon  their 
scales,  and  more  particularly  upon  aneroids  with  expanded  scales  (Hicks' 
Watkin  Patent)  the  loss  may  even  be  traced  in  successive  hours.2  The  loss 
in  the  first  hour  of  the  first  day,  so  far  as  my  observation  extends,  is  always 
greater  than  in  any  subsequent  one. 

1  I  have  observed  some  exceptional  cases  (not  quoted  in  the  table)  in  which  the  day's 
loss  has  been  less  than  a,  fifth  of  the  week's  loss. 

2  When  standing  over  these  instruments,  whilst  they  have  been  kept  at  so  moderate 
a  diminution  in  pressure  as  26  inches,  I  have  seen  the  index  move  backwards  whilst  the 
mercurial  barometer  remained  immovable. 

E 


26 


EXPERIMENTS  IN  THE  WORKSHOP. 


TABLE  SHOWING  THE  AMOUNTS  LOST  UPON  THE  MERCURIAL  BAROMETER 
IN  ONE  DAY  AND  IN  ONE  WEEK. 


Diameter 

Pressure  at 

Loss  upon  the 

Total  loss  upon 

Aneroid. 

of  instru- 

which it  was 

Mercurial  Bar. 

the  Merc.  Bar. 

ment. 

kept. 

in  one  day. 

in  one  week. 

inch. 

inch. 

inch. 

inch. 

Hicks                                   (E) 

2 

14 

0-510 

0-803 

do.          ...          (F) 

2 

» 

0-720 

1-033 

do.          .         .         .       (22) 

3 

15 

0-546 

0-701 

do.          ...       (23) 

3 

j? 

0-481 

0-746 

Casella     .         .          .  (5606) 

2 

17 

0-521 

0-727 

do.        ...  (5606) 

2 

18 

0-378 

0-463 

do.        ...  (5798) 

3 

?) 

0-513 

0-653 

do.        .         .          .  (5792) 

2 

20 

0-660 

0-767 

do.                 .         .  (5892) 

2 

5J 

0-545 

0-652 

Hicks       .         .         .       (37) 

2 

55 

0-545 

0-677 

do.         ...       (38) 

2 

55 

0-280 

0-362 

do.          .         .                 (39) 

2 

)> 

0-685 

0-842 

do.          ...       (40) 

2 

)) 

0-255 

0-337 

do.          ...       (42) 

2 

» 

0-225 

0-287 

Casella     .         .         .     (580) 

2 

21 

0-325 

0-461 

do.        ...  (1021) 

2f 

•>•> 

0-385 

0-533 

do.        .         .         .  (5793) 

2 

22 

0-342 

0-473 

do.        .         .         .  (5893) 

2 

j> 

0-227 

0-353 

Hilger      . 

2 

jj 

0-292 

0-458 

Hicks       .         .         .       (20) 

4| 

23 

0-154 

0-252 

Cooke       .         .         .     (160) 

2} 

» 

0-161 

0-264 

Hicks    (Watkin  Patent,  232) 

3 

24 

0-111 

0-273 

Casella     .         .         .  (4493) 

4 

24-5 

0-146 

0-185 

do.        .         .         .  (5682) 

3 

5) 

0-181 

0-245 

do.        .          .          .  (1842) 

4j 

?) 

0-121 

0-200 

Hicks      (Watkin  Patent,  17) 

4i 

25 

0-052 

0-144 

do.        (           do.                9) 

4 

26 

0-069 

0-087 

do.        (          do.            141) 

3 

•>•> 

0-084 

0-094 

Casella     .         .         .  (2923) 

4 

)» 

0-099 

0-132 

EXPERIMENTS  IN  THE  WORKSHOP. 


27 


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28 


EXPERIMENTS  IN  THE  WORKSHOP. 


TABLE  SHOWING  THE  AMOUNTS  LOST  UPON  THE  MERCURIAL  BAROMETER 

IN    THE    FIRST    HOUR    AND    IN    THE    FIRST    DAY. 


Aneroid. 

Diameter 
of  instrument. 

Pressure  at 
which  it  was 
kept. 

Error  on  the 
Merc.  Bar. 
(red.  to  32°)  upon 
being  reduced  to 
the  pressure  at 
which  it  was 
kept. 

Error  on  the 
Merc.  Bar. 
at  the  end  of 
the  first  hour. 

Error  on  the 
Merc.  Bar. 
at  the  end  of 
the  first  day. 

inch. 

inch. 

inch. 

inch. 

inch. 

Hicks       .         .         (E) 

2 

14 

-0-208 

-0-531 

-0-718 

do.         .          .          (F) 

2 

5) 

-0-158 

-0-596 

-0-878 

do.          .          .        (22) 

3 

15 

+  0-047 

-0-274 

-0-499 

do.         .         .       (23) 

3 

55 

+  0-247 

-0-024 

-0-234 

do.         .         .       (11) 

3 

17 

-0-604 

-0-852 

-  1-054 

do.         .         .       (12) 

3 

55 

-0-234 

-0-437 

-0-604 

do.         .                 (22) 

3 

18 

+  0-001 

-0-254 

-0-382 

do.         .         .       (23) 

3 

55 

+  0-196 

-0-004 

-0-132 

do.         .         .       (37) 

2 

20 

-0-164 

-0-526 

-0-709 

do.         .         .       (38) 

2 

55 

-0-024 

-0-126 

-0-304 

do.         .         .       (39) 

2 

55 

-0-374 

-0-676 

-  1-059 

do.         .         .       (40) 

2 

55 

+  0-676 

+  0-554 

+  0-421 

do.         .         .       (42) 

2 

55 

-0-024 

-0-086 

-0-249 

Casella     .         .  (5792) 

2 

55 

+  0-456 

+  0-124 

-0-204 

do.         .         .  (5892) 

2 

51 

+  0-066 

-0-201 

-0-479 

do.         .         .     (580) 

2 

21 

+  0-296 

+  0-184 

-0-002 

do.         .         .  (1021) 

2J 

55 

-  1-174 

-1-331 

-1-512 

do.         .         .  (5793) 

2 

22 

+  0-094 

-0-082 

-0-291 

do.         .         .  (5893) 

2 

5) 

+  0-079 

-0-057 

-0-191 

Hilger      . 

2 

55 

+  0-339 

+  0-188 

-0-006 

Hicks       .         .       (20) 

4i 

23 

+  0-056 

-0-052 

-0-098 

Cooke       .         .     (160) 

2| 

» 

+  0-353 

+  0-263 

+  0-192 

Hicks  (Watkin  P.  232) 

3 

24 

+  0-118 

+  0-069 

+  0-007 

Hicks       .          .       (32) 

2 

25 

+  0-274 

+  0-213 

+  0-118 

do.         .         .       (33) 

2 

55 

-0-121 

-0-172 

-0-207 

Casella     .         .  (2923) 

4j 

26 

+  0-155 

+  0-094 

+  0-056 

Hicks     (Watkin  P.     9) 

4 

55 

+  0-065 

+  0-029 

-0-004 

do.       (      do.        141) 

3 

5? 

+  0-065 

+  0-014 

-0-019 

do.       (      do.        165) 

4 

55 

+  0-142 

+  0-087 

+  0-024 

§  31.  From  the  foregoing  experiments  it  is  clearly  apparent  that  the 
extent  of  the  loss  which  will  occur  in  any  aneroid  upon  the  mercurial 
barometer,  upon  being  submitted  to  diminished  pressure,  depends,  1.  upon 


EXPERIMENTS  IN  THE   WORKSHOP.  29 

the  duration  of  time  it  may  be  submitted  to  diminished  pressure,  and  2. 
upon  the  extent  of  the  diminution  in  pressure  ;  and  it  follows  that  the  errors 
which  will  be  manifested  by  any  particular  aneroid  will  be  greatest  when  it 
is  submitted  to  very  low  pressures  for  long  periods.1  Consideration  of  some 
practical  conclusions  which  may  be  drawn  from  these  facts  is  deferred  to  the 
third  portion  of  this  paper,  and  I  now  proceed  to  give  some  examples  of  the 
behaviour  of  aneroids  upon  their  return  to  normal  pressure,  after  having 
experienced  diminished  pressure  for  a  length  of  time. 

§  32.  The  first  series  which  was  experimented  upon  (Nos.  1-6)  was 
watched  by  me  for  twenty-one  weeks  after  being  allowed  to  return  to  the 
natural  pressure  of  the  time ;  and  it  was  found  that  the  large  mean  error  which 
existed  at  the  termination  of  the  experiment,  namely  -  0*325  of  an  inch  (see 
table  on  p.  1 7),  gradually  lessened,  and  that  on  the  expiration  of  the  twelfth 
week  the  six  aneroids  had  'recovered'  all  they  had  previously  lost  The 
mean  error  at  the  commencement  of  the  experiment  was  +0'048,  and  at 
the  end  of  the  twelfth  week  (after  return  to  natural  pressure)  it  stood  at 
+  0-057  of  an  inch.2  In  nine  succeeding  weeks  I  was  unable  to  trace  any 
material  change  in  the  mean  index-error. 

The  three  aneroids  Nos.  10,  11,  12,  which  were  employed  in  the  second 
experiment  (see  p.  18),  were  watched  by  me  for  sixteen  weeks  after  return  to 
normal  pressure.  Their  very  large  mean  error  of  —  0'854  was  gradually 
reduced, — at  the  end  of  the  first  week  to  —  0'223,  at  the  end  of  the  second 
week  to  —  0  •  1 5 1 ,  and  so  on,  until  at  the  end  of  the  fifth  week  it  stood  at 
-  O'llO  of  an  inch.  After  this  no  farther  recovery  could  be  traced. 

§  33.  In  these  two  experiments,  and  in  all  such  succeeding  ones  as  ex- 
tended over  a  number  of  weeks,  it  was  clear  that  the  greater  part  of  the 
recovery  occurred  within  the  first  week  after  return  to  normal  pressure,  and 
I  accordingly  endeavoured  to  learn  within  what  space  of  time  the  most  im- 
portant part  of  the  loss  was  recovered.  With  this  view,  I  watched  the 
recovery  of  a  number  of  aneroids  (of  various  diameters,  by  several  makers, 
which  had  been  kept  at  different  pressures)  upon  each  day  during  a  week, 
and  observed  the  errors  of  the  aneroids  upon  the  mercurial  barometer  on 
each  successive  day.  See  table  upon  p.  30. 

§  34.  From  these  observations,  I  found  that  the  greater  part  of  the 
recovery  which  occurred  during  the  first  week  after  return  to  normal 
pressure  took  place  in  the  first  day  of  the  week;  and  that  the  amount 
recovered  in  the  first  hour  of  the  first  day  was  always  considerable,  and 
was  almost  always  greater  than  the  amount  still  further  recovered  in 
any  subsequent  hour.  See  table  upon  p.  31. 

1  The  loss  is  not  strictly  proportional  throughout  the  whole  length  of  the  scale  of  any 
aneroid,  and  at  the  last  (or  lowest)  inch  of  the  graduation  it  is  sometimes  much  greater 
than  at  any  other  part  of  the  scale.     It  is  not  advisable  to  attempt  to  work  an  aneroid  to 
the  full  extent  of  its  range. 

2  The  most  important  part  of  the  recovery  occurred  much  earlier. 


30  EXPERIMENTS  IN  THE  WORKSHOP. 

TABLE  SHOWING  THE  AMOUNTS  RECOVERED  IN  ONE  DAY  AND  IN  ONE  WEEK. 


Aneroid. 

Diameter 
of  instrument. 

Pressure  at  which 
it  was  kept  for  one 
week. 

1. 

Error  on  the 
Merc.  Bar. 
at  natural 
pressure 
before 
reduction  of 
pressure. 

2. 

Error  on  the 
Merc.  Bar. 
on  return 
to  normal 
pressure. 

3. 

Error  on  the 
Merc.  Bar. 
one  day 
later. 

4. 

EiTor  on  the 
Merc.  Bar. 
one  week 
later. 

inch. 

inch. 

inch. 

inch. 

inch. 

inch. 

Hicks    .         .         (E) 

2 

14 

+  0-248 

-0-238 

+  0-143 

+  0-213 

do.       .         .         (F) 

2 

„ 

+  0-098 

-0-598 

+  0-013 

+  0-098 

do.       .          .        (22) 

3 

15 

-0-036 

-0-360 

-0-050 

+  0-006 

do.       .          .        (23) 

3 

„ 

-0-206 

-0-560 

-0-265 

-0-209 

Cary      .         .     (732) 

2f 

17 

+  0-142 

-0-379 

-0-213 

-0-198 

do.        .         .     (829) 

2} 

„ 

+  0-182 

-0-539 

-0-288 

-0-223 

do.        .         .     (841) 

2f 

55 

+  0-442 

-  1-029 

-0-163 

+  0-052 

Casella  .         .  (5606) 

2 

18 

+  0-158 

-0-220 

+  0-062 

+  0-090 

do.      .         .  (4885) 

2 

„ 

+  0-113 

-  0-087 

+  0-130 

+  0-174 

do.      .         .  (5798) 

3 

„ 

+  0-058 

-0-430 

-0-113 

-0-075 

Cooke    .         .     (170) 

4 

„ 

-0-237 

-0-537 

-0-295 

-0-201 

Secretan 

4.1 

+  0-029 

-0-028 

+  0-057 

+  0-068 

Hicks    .                 (37) 

2 

20 

+  0-080 

-0-547 

-0-092 

+  0-028 

do.       .                 (38) 

2 

„ 

-0-065 

-0-407 

-0-187 

-0-092 

do.       .         .       (39) 

2 

55 

-0-140 

-0-977 

-0-457 

-0-317 

do.       .          .       (40) 

2 

55 

+  0-415 

+  0-263 

+  0-558 

+  0-708 

do.       .         .       (42) 

2 

55 

-0-105 

-0-272 

-0-162 

-0-072 

Casella  .         .  (5792) 

2 

55 

+  0-245 

-0-237 

+  0-068 

+  0-158 

do.      .         .  (5892) 

2 

55 

+  0-110 

-0-222 

-0-052 

+  0-043 

do.      .         .     (580) 

2 

21 

+  0-351 

-0-098 

+  0-199 

+  0-298 

do.      .          .  (1021) 

2| 

55 

-1-249 

-1-848 

-1-526 

-  1-332 

Hilger  . 

2 

22 

+  0-180 

-0-281 

+  0-013 

+  0-054 

Casella  .         .  (5793) 

2 

55 

+  0-010 

-0-356 

-0-087 

-0-021 

do.      .         .  (5893) 

2 

55 

+  0-180  i   -0-056 

+  0-083 

+  0-129 

Cooke    .         .     (160) 

2f 

23 

-0-036 

-0-191 

-0-049 

-0-025 

Hicks    .         .       (20) 

4j 

55 

+  0-014 

-0-166 

-0-069 

-0-013 

Hicks  (Watkin  P.  2  3  2) 

3 

24 

-0-022 

-0-169 

-0-105 

-0-074 

Hicks    .         .       (29) 

2 

25-2 

-0-209 

-0-507 

-0-414 

-0-310 

do.       .         .       (31) 

2 

55 

+  0-166 

+  0-023 

+  0-136 

+  0-160 

do.       .         .       (32) 

2 

55 

+  0-161 

-0-017 

+  0-056 

+  0-200 

do.       .         .       (33) 

2 

55 

-0-179 

-0-277 

-0-209 

-0-200 

do.       .         .       (35) 

2 

55 

+  0-266 

+  0-203 

+  0-306 

+  0-345 

Hicks  (Watkin  P.     9) 

4j 

26 

+  0-013 

-0-045 

+  0-048 

+  0-059 

do.    (      do.        141) 

3 

55 

-0-037 

-0-155 

-0-050 

-0-020 

Casella  .         .  (2923) 

4! 

55 

+  0-093 

+  0-005 

+  0-095 

+  0-103 

Hicks  (Watkin  P.  165)    4j 

+  0-039 

-0-163 

-0-061 

+  0-005 

EXPERIMENTS  IN  THE  WORKSHOP. 


31 


TABLE  SHOWING  THE  AMOUNTS  RECOVERED  IN  ONE  HOUR  AND  IN  ONE  DAY. 


Aneroid. 

Diameter 
of  instrument. 

Pressure  at 
which  it  was  kept 
for  one  week. 

Error  on  the 
Merc.  Bar. 
at  natural 
pressure 
before 
reduction  of 
pressure. 

Error  on  the 
Merc.  Bar. 
on  return 
to  normal 
pressure. 

Error  on  the 
Merc.  Bar. 
one  hour 
later. 

Error  on  the 
Merc.  Bar. 
one  day 
later. 

inch.1  inch. 

inch. 

inch. 

inch. 

inch. 

Hicks    .          .          (E) 

2 

14 

+  0-248 

-0-238 

+  0-012 

+  0-143 

do.       .          .          (F) 

2 

33 

+  0-098 

-0-598 

-0-278 

+  0-013 

do.       .                  (22) 

3 

15 

-0-036 

-0-360 

-0-250 

-0-050 

do.       .          .        (23) 

3 

33 

-0-236 

-0-560 

-0-470 

-0-265 

Casella  .          .  (5606) 

2 

18 

+  0-158 

-0-220 

-0-043 

+  0-062 

do.      .          .  (5798) 

3 

33 

+  0-058 

-0-430 

-0-283 

-0-113 

do.      .          .  (5792) 

2 

20 

+  0-245 

-0-237 

-0-059 

+  0-068 

do.      .          .  (5892) 

2 

33 

+  0-110 

-0-222 

-0-144 

-0-052 

Hicks    .          .       (37) 

2 

3) 

+  0-080 

-0-547 

-0-234 

-0-092 

do.       .          .       (38) 

2 

3) 

-0-065 

-0-407 

-0-274 

-0-187 

do.       .          .       (39) 

2 

3) 

-0-140 

-0-977 

-0-664 

-0-457 

do.       .          .       (40) 

2 

33 

+  0-415 

+  0-263 

+  0-291 

+  0-558 

do.       .          .        (42) 

2 

33 

-0-105 

-0-.272 

-0-214 

-0-162 

Hilger  . 

2 

22 

+  0-180 

-0-281 

-0-084 

+  0-013 

Casella  .          .  (5793) 

2 

33 

+  0-010 

-0-356 

-0-214 

-0-087 

do.      .          .  (5893) 

2 

33 

+  0-180 

-0-056 

+  0-016 

+  0-083 

Cooke    .          .     (160) 

2f 

23 

-0-036 

-0-191 

-0-108 

-0-049 

Hicks    .          .        (20) 

4 

33 

+  0-014 

-0-166 

-0-108 

-0-069 

Hicks(WatkinP.232) 

3 

24 

-  0-022 

-0-169 

-0-112 

-0-105 

do.    (      do.         165) 

*J 

26 

+  0-039 

-0-163 

-0-102 

-0-061 

§  35.  From  examination  of  the  whole  of  the  observations  upon  the 
recovery  I  find  : — 

That  the  greater  the  length  of  time  during  which  aneroids  may  be  sub- 
mitted to  a  reduction  of  pressure  the  greater  is  the  length  of  time  over  which 
their  recovery  extends. 

That,  in  instances  where  aneroids  have  been  kept  continuously  at 
diminished  pressures  for  a  month  and  upwards,  the  greater  part  of  the 
recovery  that  occurs  takes  place  in  the  first  iveek  after  return  to  normal 
pressure. 

That,  in  instances  where  aneroids  have  been  kept  continuously  at 
diminished  pressures  for  a  week,  the  greater  part  of  the  recovery  which  occurs 
in  the  first  week  after  return  to  normal  pressure  usually  takes  place  within 
the  first  day. 

That  the  amount  recovered  in  the  first  hour  is  almost  always  larger  than 
the  amount  still  further  recovered  in  any  subsequent  hour.1 

1  The  exceptions,  have  been  very  few. 


32  EXPERIMENTS  IN  THE  WORKSHOP. 

That  the  total  amount  recovered  very  seldom  exactly  equals  the  total 
amount  previously  lost,  and  is  sometimes  less  and  sometimes  greater  than  it. 
There  are  consequential  changes  in  the  index-error  of  aneroids. 

§  36.  It  can  be  seen  from  the  observations  already  quoted  that  there  are 
frequent  changes  in  the  initial  index-errors  of  aneroids.  If,  for  example, 
Col.  4  of  the  table  on  p.  30  is  compared  with  Col.  1,  it  will  be  noticed  that 
twelve  aneroids  out  of  the  thirty -six  which  are  there  reported  upon — 
those  marked  by  asterisks — recovered,  in  a  week,  the  whole  of  the  amounts 
which  they  had  previously  lost  in  a  week  at  the  mentioned  pressures,  and 
gained  something  more.  The  twelve  all  read  higher  at  the  expiration  of  one 
week  after  return  to  normal  pressure  than  they  read  before  reduction  of 
pressure.  At  the  end  of  one  week  they  had  not  completed  their  '  recovery.' 
If  the  whole  thirty-six  instruments  had  been  watched  it  would  probably 
have  been  found  that  they  continued  to  gain  (though  in  minute  quantities) 
for  several  weeks  longer,  and  at  the  expiration  of  a  month  there  would  have 
been  about  half  of  them  reading  higlier  than  before  reduction  of  pressure  (in 
comparison  with  the  Mercurial  Barometer),  and  the  rest  reading  lower  than 
before  reduction  of  pressure. 

§  37.  The  considerable  length  of  time  over  which  the  'recovery'  ex- 
tends, and  the  frequency  in  alteration  of  index-errors,  will  perhaps  be  better 
apprehended  by  inspection  of  the  table  on  p.  33.  In  an  experiment  (which 
will  be  referred  to  in  Part  3  l)  I  kept  twenty -two  aneroids  at  a  pressure  of 
21*692  inches  for  a  week,  and  watched  the  behaviour  of  the  instruments 
for  thirty  days  after  their  return  to  normal  pressure.  In  Col.  2  of  the 
table  the  errors  are  stated  that  these  twenty-two  aneroids  possessed  immedi- 
ately before  reduction  of  pressure.  In  Col.  3  the  errors  are  stated  which 
they  were  found  to  have  immediately  after  restoration  of  pressure.  In  Col.  4 
their  errors  fourteen  hours  later,  and  so  on.  If  the  eye  is  carried  along 
each  line,  from  left  to  right  across  the  page,  it  will  be  seen  that  there  is  a 
continual  lessening  of  minus  errors  and  increase  in  plus  ones,  showing  that 
recovery  was  still  proceeding  after  the  twelfth  day.  Then,  if  the  eye  is 
carried  down  the  columns,  it  will  be  found  that  immediately  after  restoration 
of  pressure  one  aneroid  already  read  higher  than  it  did  before  reduction  of 
pressure.  In  Col.  4  there  are  five  which  read  higher  ;  in  Col.  5  there  are 
nine,  and  in  Col.  6  there  are  sixteen,  marked  by  asterisks. 

§  38.  In  some  of  the  aneroids  which  have  been  under  examination  for 
years,  and  have  been  employed  in  numerous  experiments,  I  have  noticed  a 
continual  tendency  to  augmentation  of  error  in  the  +  direction,  whilst  in 
others  there  has  been  a  continual  tendency  in  the  —  direction  ;  or,  to  employ 
a  term  which  is  used  in  connection  with  other  instruments,  some  have 
appeared  to  have  a  gaining  and  others  to  have  a  losing  rate.  It  seems  to 
me,  also,  that  a  gaining  rate  not  unfrequently  changes  to  a  losing  one,  or 
the  contrary  ;  but  upon  this  point  I  speak  with  hesitation,  through  having 
been  unable  to  retain  instruments  for  a  length  of  time  sufficient  to  arrive 
at  definite  conclusions. 

1  See  pp.  37-39. 


EXPERIMENTS  IN  THE   WORKSHOP. 


33 


TABLE  SHOWING  THE  '  RECOVERY  '  OP  22  ANEROIDS  UP  TO  THE  END  OF  30  DAYS 

(AFTER  THEY  HAD  BEEN  SUBMITTED  TO  A  PRESSURE  OF  21-692  INCHES 

FOR  ONE  WEEK),  AND  THE  ALTERATIONS  IN  THEIR  INDEX-ERRORS. 


1. 

2. 

3. 

4. 

5. 

6. 

Maker's  name  and 
mark. 

Index-error 
at  natural 
pressure  be- 
fore reduction 

Index-error 
after  pressure 
was  restored. 

Index-error 
14  hours  after 
pressure  was 
restored. 

Index-error 
12  days  after 
pressure  was 
restored. 

Index-error 
30  days  after 
pressure  was 
restored. 

of  pressure. 

inches. 

inches. 

inches. 

inches. 

inches. 

Hicks     .          (1) 

+  0-013 

-0-262 

-0-074 

-0-071 

+  0-100 

»         •          (2) 

+  0-033 

-0-202 

-0-044 

+  0-049 

+  0-145 

(3) 

+  0-103 

-0-067 

+  0-106 

+  0-129 

+  0-170 

»         •          (4) 

+  0-073 

-0-172 

-0-044 

-0-016 

+  0-140 

„         .          (5) 

-0-032 

-0-342 

-0-154 

-0-101 

-0-040 

(6) 

+  0-103 

-0-092 

+  0-046 

+  0-059 

+  0-120 

„          •          (F) 

+  0-248 

+  0-133 

+  0-276 

not 

observed 

(9) 

+  0-133 

+  0-008 

+  0-136 

+  0-149 

+  0-190 

Casella  .     (580) 

+  0-483 

+  0-138 

+  0-376 

+  0-399 

+  0-455 

Hicks     .       (37) 

+  0-078 

-0-162 

+  0-046 

+  0-129 

+  0-160 

.       (38) 

-0-057 

-0-192 

-0-074 

-0-056 

+  0-005 

.       (39) 

-0-137 

-0-592 

-0-249 

-0-151 

-0-070 

„         -       (40) 

+  0-478 

+  0-333 

+  0-416 

+  0-349^ 

+  0-470 

+  0-343 

+  0-278 

+  0-301 

+  0-259<* 

+  0-360 

»         •       (42) 

-0-007 

-0-122 

+  0-006 

+  0-024 

+  0-075 

•       (10) 

-0-177 

-0-517 

-0-274 

-0-231 

-0-160 

„         •       (11) 

-0-407 

-0-607 

-0-499 

-0-441 

-0-450^ 

•       (12) 

-0-077 

-0-222 

-0-104 

-0-091 

-0-060 

Hilger    . 

+  0-028 

-0-182 

-0-004 

+  0-034 

+  0-120 

Hicks     .          (8) 

+  0-253 

+  0-308 

+  0-466 

+  0-499 

+  0-505 

Casella  .  (1021) 

-1-117 

-  1-602 

-1-384 

-1-296 

-1-245 

Cooke    .     (170) 

-0-227 

-0-422 

-0-249 

-0-186 

-0-140 

d  Discordant. 

§  39.  These  alterations  in  the  index-errors  of  aneroids  are  doubtless  con- 
tinually going  forward  under  the  natural  variations  of  atmospheric  pressure 
which  occur  everywhere.  From  a  single  fluctuation  of,  say,  an  inch,  the  gain 
or  loss  may  be  so  small  as  to  be  imperceptible  ;  but  in  course  of  time  they 
mount  up  and  begin  to  tell,  and  in  this  way  aneroids  acquire  (as  many  per- 
sons must  have  remarked)  considerable  +  or  —  errors  when  put  away  in 
drawers,  and  repose,  so  to  speak,  out  of  use. 

From  the  foregoing  experimental  comparisons  of  the  aneroid  against  the 
mercurial  barometer  in  the  workshop  it  will  be  seen  that  one  may  be  led 
into  very  serious  errors  in  observing  variations  of  pressure  by  the  employ- 
ment of  aneroids.  1.  By  reason  of  the  loss  upon  the  mercurial  which  com- 

F 


34  EXPERIMENTS  IN  THE  WORKSHOP. 

mences  immediately  pressure  is  reduced,  or,  2.  through  the  recovery  which 
sets  in  immediately  pressure  is  restored  ;  or,  3.  by  the  changes  in  index-errors 
which  are  continually  happening.1 

I  have  thought  it  advisable  in  the  present  part  of  the  paper  to  confine 
myself  as  closely  as  possible  simply  to  comparisons  of  the  indications  of  the 
two  classes  of  barometer,  without  regard  to  the  uses  to  which  observations  of 
differences  in  atmospheric  pressure  may  be  applied.  The  determination  of 
altitudes  is  amongst  the  most  important  of  these  uses,  and  in  Part  3  I  venture 
to  offer  a  few  remarks  upon  this  subject. 

i 

1  At  the  commencement,  I  employed  the  apparatus  which  was  in  daily  use  at  Mr. 
Hicks'  establishment.  It  was  soon  found  necessary  to  duplicate  this  in  order  to  facilitate 
progress,  and  subsequently  I  set  up  a  similar  apparatus  in  my  own  workshop.  It  became 
necessary  also  to  duplicate  this,  and  finally  I  had  a  receiver  30  inches  high  constructed, 
in  order  to  have  twenty  or  more  aneroids  under  examination  at  one  time. 

Upon  going  one  day  to  Mr.  Hicks'  establishment,  I  found  the  aneroid  department  in 
some  confusion,  and  learned  that  just  before  my  arrival  an  accident  had  happened  to  an 
apparatus  which  we  were  keeping  experimentally  at  a  pressure  of  16  inches.  With  a 
report  like  a  rifle,  plate  glass  more  than  a  quarter  of  an  inch  thick  was  crushed  in  by 
the  external  pressure,  and  rebounded  in  a  multitude  of  fragments  over  the  room.  The 
apparatus  was  shattered,  and  an  attached  mercurial  barometer  was  destroyed, 

Mr.  Murray,  the  head  of  the  department,  was  close  by  at  the  time,  and  said  ib 
seemed  to  him  like  an  explosion,  as  he  only  saw  the  rebounding  splinters  flying  in  all 
directions.  As  soon  as  it  could  be  done,  Mr.  Hicks  replaced  this  apparatus  at  his  own 
cost,  and  the  experiment  was  recommenced. 

In  all  the  experiments  made  at  Mr.  Hicks'  establishment,  the  mercurial  barometers; 
were  first  read  by  Mr.  Murray  and  the  aneroids  were  read  by  myself.  We  then  checked 
each  other's  readings. 


PART  3. 

UPON   THE   USE  OF  THE  ANEROID   BAROMETER 
IN    DETERMINATION   OF  ALTITUDES. 

In  the  second  part  of  this  paper  it  has  been  shown,  1.  that  aneroids  lose 
upon  the  mercurial  barometer  when  submitted  to  diminished  pressure ;  2.  that 
aneroids  recover  some  portion  of  this  loss  upon  restoration  of  pressure  ;  and 
3.  that  there  are  frequent  changes  in  the  index-errors  of  aneroids.  From  the 
most  cursory  inspection  of  this  part  of  the  paper  it  will  be  apparent  that  an 
observer  in  the  field,  endeavouring  to  determine  altitudes  above  the  sea-level 
by  comparison  of  aneroid  readings  against  barometric  observations  at  lower 
stations,  may  be  (and  often  must  be)  led  into  very  serious  errors  through 
these  several  causes.  In  the  remarks  which  follow  I  shall  endeavour  to  show 
some  ways  in  which  this  liability  to  error  may  be  guarded  against. 

§  40.  When  an  aneroid  experiences  diminished  pressure  (as  it  does  when 
a  traveller  is  ascending)  it  at  once  commences  to  lose  upon  the  mercurial 
barometer,  and  to  indicate  a  greater  diminution  of  pressure  than  the  truth.1 
The  traveller  is  thus  led  to  overestimate  his  altitude,  no  matter  whether  he 
attempts  to  gain  an  idea  of  it  by  mere  inspection  of  the  aneroid,  or  by  com- 
paring the  aneroid  readings  with  other  barometric  readings  at  lower  stations. 
This  tendency  to  lose  continues  for  several  weeks.  When  it  ceases  (and  it 
will  cease  in  a  few  weeks  at  a  constant  pressure)2  the  aneroid  will  then 
indicate  the  natural  (diurnal  or  hourly)  fluctuations  in  atmospheric  pressure 
almost  as  accurately  as  the  mercurial  barometer  itself ;  but,  until  it  ceases, 
natural  (diurnal  or  hourly)  variations  in  atmospheric  pressure  cannot  be  accurately 
observed  from  aneroids.  It  may,  indeed,  happen  that  the  index  of  an  aneroid 
may  be  falling  (or  indicating  diminution  in  pressure)  at  a  time  that  pressure  is 
actually  increasing. 

§  41.  When  an  aneroid  experiences  restoration  of  pressure  (after  having, 
previously,  experienced  diminished  pressure)  it  at  once  commences  to  recover, 
or  regain,  its  previous  loss.  This  recovery  almost  always  goes  on  for  several 
weeks,  and  when  it  ceases  (but  not  until  then)  the  aneroid  will  again  indicate 
natural  (hourly  or  diurnal)  variations  with  reasonable  accuracy. 

1  It  is  assumed  in  the  remarks  throughout  this  part  of  the  paper  that  aneroids  are 
correctly  graduated,  and  read  truly  against  the  mercurial  barometer  when  pressure  is 
reduced  instantaneously. 

2  And  the  loss  will  recommence,  and  proceed  as  before,  if  the  aneroid  is  taken  to  a 
greater  elevation  (that  is,  experiences  still  lower  pressure). 


36  UPON  THE  USE  OF  THE  ANEROID  BAROMETER 

§42.  The  tendency  to  lose,  and  to  recover,  is  most  active  during  the 
first  day  of  change  of  pressure,  but  it  is  well  marked  for  several  days  (see 
table  on  p.  27).  Hence  aneroids  which  may  be  employed  by  travellers  at 
upper  or  lower  stations  (with  the  view  of  applying  corrections  to  simultaneous 
observations  at  lower  or  upper  stations)  ought  to  be  installed  at  such  upper  or 
lower  stations  for  several  days  before  being  used  for  simultaneous  observations. 

§  43.  If  an  aneroid  should  be  taken  to  some  lofty  position  (thereby  ex- 
periencing diminution  of  pressure),  and  should  be  allowed  to  remain  there  for 
several  weeks,  it  will  get  into  what  may  be  termed  "  a  condition  of  repose." 
If  the  diminution  in  pressure  is  large,  the  instrument  will  certainly  acquire 
a  considerable  error  ;  but  at  the  end  of  a  few  weeks  this  error  will  remain 
tolerably  constant,1  so  long  as  the  aneroid  remains  at  one  level  (that  is,  at  a 
nearly  constant  pressure)  ;  and,  if  it  should  then  be  used  rapidly,  the  differ- 
ences of  pressure  which  will  be  indicated  by  it  will  closely  accord  with  those 
which  would  be  indicated  by  a  mercurial  barometer,  as  the  error  will  be  carried 
along  the  scale? 

§  44.  The  fact  that  aneroids  which  have  acquired  large  index-errors  may 
nevertheless  (under  certain  conditions)  be  usefully  employed  for  measurement 
of  differences  of  level  is  one  of  great  importance  to  travellers  or  surveyors, 
who  must,  however,  always  bear  in  mind  the  best  results  will  be  attained  when 
the  least  possible  amount  of  time  intervenes  between  the  readings  at  two  stations 
upon  different  levels. 

§  45.  The  fact  that  index-errors  are  commonly  carried  along  the  scale 
when  observations  are  made  with  rapidity  accounts  for  some  of  the  remark- 
able agreements  which  were  observed  in  Ecuador,  and  I  propose  to  revert 
for  a  few  minutes  to  the  instance  mentioned  in  §  12.  On  the  journey  to  the 
north  of  Quito,3  I  carried  Merc.  Bar.  No.  558,  and  aneroids  A  and  B,  and 
upon  arrival  at  the  top  of  the  great  ravine  of  Guallabamba  took  simultaneous 
observations  of  the  mercurial  and  aneroids.  At  the  bottom  of  the  ravine, 
two  hours  and  a  half  later,  readings  of  all  three  were  repeated  with  the 
following  result : — 

Date.  Barometer.  Read  at  top.  Read  at  bottom. 

Mar.  27,  1880  Merc.  bar.  558  (red.  to  32°  Faht)     21-692  23-929 

do.  Aneroid  A  21-140  23-400 

do.  do.      B  19-940  22-200 


The  rise  of  the  Mercurial  Barometer  was  2-237  inches, 
do.         do.     Aneroid  A  „     2-260       „ 

do.         do.  B  2-260 


1  But  not  perfectly  so.     It  has  been  pointed  out  in  §  39  that  long-continued  diurnal 
fluctuations  in  pressure  (although  small)  may  in  course  of  time  produce  marked  changes 
in  index-errors. 

2  This  will  be  illustrated  experimentally  a  few  pages  later. 

3  See   Travels  amongst  the  Great   Andes  of  the  Equator,  chap,  xii,  and  §  12  of 
this  paper. 


IN  DETERMINATION  OF  ALTITUDES.  37 

In  this  instance,  two  aneroids,  one  of  them  having  an  index -error  of 
more  than  half  an  inch,  and  the  other  having  an  index-error  of  about  one 
inch  and  three-quarters,  were  employed  for  a  measurement  of  difference  of 
level.  The  two  aneroids  indicated  precisely  the  same  difference  of  pressure 
between  the  upper  and  lower  stations,  and  differed  only  one  per  cent  from  the 
difference  of  pressure  indicated  by  the  mercurial.  How  are  these  facts  to  be 
accounted  for  ? 

They  appear  to  me  to  be  explicable  in  the  following  manner.  The  large 
index-errors  were  the  result  of  the  invariable  "loss  upon  the  mercurial" 
which  takes  place  in  aneroids  upon  sustaining  diminished  pressure,  added  to 
the  change  in  index-error  which  frequently  accumulates  when  aneroids  are 
subjected  to  large  and  frequent  fluctuations  of  pressure.  Prior  to  March  27, 
the  two  aneroids  had  remained  for  more  than  four  weeks  at  Quito  at  a  nearly 
constant  pressure  of  21-600  inches,  and  had  thus  got  into  "  a  state  of  repose." 
Their  index-errors  were  remaining  constant,  and  the  instruments  were  affected 
by  the  small  diurnal  variations  in  pressure,  which  occurred  at  Quito,  in  the 
same  way  as  the  mercurial  barometers.  If  upon  arriving  at  the  edge  of  the 
ravine  they  could  have  been  transported  instantaneously  to  the  bottom  of  it, 
the  difference  in  pressure  which  they  would  have  indicated  would,  I  do  not 
doubt,  have  almost  exactly  coincided  with  that  indicated  by  the  mercurial 
barometer.  The  fact  was  they  indicated  a  difference  in  pressure  0*023  of 
an  inch  more  than  the  mercurial,  and  this  excess  I  attribute  to  the  tendency 
to  '  recover '  which  sets  in  immediately  upon  restoration  of  pressure. 

This  experience  left  a  strong  impression  upon  my  mind.  I  have  repeated 
the  experiment  in  the  workshop  with  the  following  results. 

§  46.  I  took  twenty-two  aneroids  (purposely  including  amongst  them 
those  having  the  largest  index-errors  that  could  be  found  amongst  the  in- 
struments which  were  available)  and  reduced  them  to  a  pressure  of  21*692 
inches  (the  pressure  at  the  top  of  the  ravine  of  Guallabamba).  I  kept  them 
constantly  at  this  pressure  for  one  week  (so  that  the  greater  part  of  the  "  loss 
upon  the  mercurial"  might  occur),1  and  then  gradually  restored  pressure 
during  two  and  a  half  hours,  until  it  stood  at  23 '929  inches  (the  pressure  at 
the  bottom  of  the  ravine  of  Guallabamba).  In  Column  1  of  the  annexed 
table  the  readings  are  given  which  were  taken  before  reduction  of  pressure, 
and  in  Col.  2  the  various  errors  of  the  aneroids  at  that  time.  In  Col.  3 
the  readings  of  the  aneroids  are  given  which  were  taken  one  week  after 
they  had  been  reduced  to  21-692  inches,  and  in  Col.  4  the  various  errors 
of  the  aneroids  at  that  time.  In  Col.  >5  the  readings  are  given  which 
were  taken  when  the  mercurial  barometer  indicated  a  pressure  of  23*929 
inches,  and  in  Col.  6  the  rise  is  stated  which  was  indicated  by  all  the 
barometers  (the  differences  between  the  readings  in  Cols.  3  and  5).  In 
Cols.  7  and  8  the  readings  and  errors  are  given  upon  return  to  natural 
pressure. 

1  To  have  repeated  the  conditions  of  the  experiment  in  the  field,  these  aneroids 
should  have  been  kept  at  21*692  inches  for  four  or  more  weeks.  There  were  other 
demands  upon  my  apparatus  at  the  time,  which  prevented  me  from  doing  so. 


38  UPON  THE  USE  OF  THE  ANEROID  BAROMETER 


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•  IN  DETERMINATION  OF  ALTITUDES.  39 

The  immediate  object  of  this  experiment  was  to  see  how  repetition  in 
the  workshop  would  accord  with  the  experience  in  the  field.  It  will  be 
found  that  it  agreed  in  a  remarkable  manner.  The  mean  of  the  whole  of 
the  aneroid  differences  in  Col.  6  is  2*218  inches  *  or,  if  the  reading  of 
No.  1021  (Casella)  is  rejected,1  and  the  mean  is  taken  of  the  twenty-one 
others,  it  will  be  found  to  be  2*231  inches, — a  difference  of  only  six- 
thousandths  of  an  inch  from  the  rise  in  pressure  indicated  by  the  mercurial 
barometer.  If  the  aneroid  observations  are  taken  singly,  it  will  be  found 
that  six  of  them  differ  from  the  mercurial  barometer  only  to  the  extent 
of  0*018  of  an  inch  or  less,  and  that  the  extremes  (rejecting  No.  1021) 
are  2-130  and  2*360  inches. 

From  this  experiment  (as  well  as  from  many  others)  it  appears  that 
although  aneroids  under  diminished  pressure  acquire  considerable  index  - 
errors,  and  often  acquire  huge  ones  under  a  long  continuance  of  largely 
diminished  pressure  combined  with  frequent  fluctuations  in  pressure,  they 
still  continue  to  march  inch  by  inch  with  the  mercurial  barometer  ;  and 
upon  a  single  operation  involving  a  difference  of  pressure  even  of  several 
inches  may  come  very  near  to  the  truth,  provided  the  operation  is 
quickly  performed. 

§  47.  The  correct  measurement  of  differences  of  pressure  is,  however, 
only  a  step  in  the  barometric  determination  of  differences  of  level.  Every 
inch  of  the  barometer  has  its  own  special  value  in  calculations  of  alti- 
tude. The  inch  embraced  between  31  and  30  inches  is  worth  about  894 
feet,  while  that  between  15  and  14  inches  is  worth  about  1880  feet. 
In  order  to  ascertain  differences  of  level  correctly  it  is  necessary  for  an 
observer  to  know  not  only  the  difference  of  pressure  but  also  the  par- 
ticular inches  embracing  his  difference  of  pressure.  The  value  in  English 
feet  of  the  difference  between  19*940  and  22*200  inches  (the  readings  of 
aneroid  B  at  the  ravine  of  Guallabamba)  is  ten  per  cent  greater  than  the 
value  of  the  difference  between  21*692  and  23*929, — the  readings  of 
the  mercurial  barometer.2  Even  for  measurement  of  differences  of  level,  it  is 
highly  desirable  that  a  traveller  should,  at  all  times,  have  the  means  of  ascer- 
taining the  index-errors  of  his  aneroids. 

§  48.  The  importance  of  being  able  to  do  this  is  far  greater  in  observa- 
tions for  determination  of  elevation  above  the  level  of  the  sea.  The  mistake 
which  the  index-error  of  an  aneroid  then  introduces  into  calculations  is  the 
whole  value  of  the  difference  of  its  readings  at  the  upper  station  from  the 
true  barometric  reading.3  Aneroid  B,  at  the  top  of  the  ravine  of  Gualla- 

1  As  it  fairly  may  be.     This  is  an  old  aneroid,  which,  prior  to  this  experiment, 
had  been  reposing  in  a  drawer  for  about  eighteen  years,  and  did  not  work  freely. 

2  For  the  purposes  of  this  passage,  and  for  all  the  computations  which  have  been 
necessary  throughout   this   paper   of  the   value   of  the   barometric   inch   at   different 
pressures,  I  have  used  the  Table  prepared  at  the  Royal  Observatory,  Greenwich,  en- 
titled   Corresponding   Numbers   of  Elevation   in   English   Feet,  and   of  Readings   of 
Aneroid  or  Corrected  Barometer  in  English  Inches  ;   the  Mean  of  Atmospheric  Tem- 
peratures being  50°  Fahrenheit.     See  pp.  56,  57. 

3  See  the  last  columns  of  the  tables  upon  pp.  21-24, 


40  UPON  THE   USE  OF  THE  ANEROID  BAROMETER 

bamba,  read  19*940  and  the  mercurial  barometer  21'692  inches.  The 
difference  of  these  two  readings  is  1-752  inches,  and  the  value  of  this,  at  the 
elevation  in  question,  is  above  2000  feet.  Although  this  is  a  gross  case, 
more  extreme  ones  are  possible. 

§  49.  I  desire  to  lay  especial  stress  upon  the  changes  which  occur  in  the 
index-errors  of  aneroids.  From  prolonged  observation,  it  appears  to  me  that 
they  seldom  remain  stationary,  and  are  never  permanent.  They  take  place 
from  a  variety  of  causes.  In  the  course  of  my  experiments  in  the  workshop 
I  have  seen  the  index-errors  of  an  aneroid  grow  to  as  much  as  four  inches  ; 
in  several  instances  there  have  been  alterations  of  more  than  an  inch  ;  and 
in  numerous  instruments  there  have  been  alterations  from  scarcely  appreciable 
errors  to  4-  or  —  errors  of  two  to  four-tenths  of  an  inch.1  Even  the  least  of 
these  amounts  (0'200  of  an  inch)  is  of  consequence  in  the  calculation  of  alti- 
tudes, and  it  has  a  considerable  value  when  great  heights  (low  pressures)  are 
concerned. 

The  continual  variations  which  occur  in  the  index-errors  of  aneroids  have 
not,  I  think,  hitherto  been  sufficiently  recognized.  Index-errors  have  gener- 
ally been  treated  as  if  they  remained  constant ;  and,  to  correct  them,  it  has 
been  considered  sufficient  to  apply  as  constant  corrections  (perhaps  for  the 
space  of  years)  the  amounts  stated  in  "  certificates  of  examination."  These 
certificates  2  have  a  very  limited  value.  They  point  out,  no  doubt  correctly, 
the  errors  which  were  exhibited  at  the  time  of  examination ;  and,  if  the  certi- 
fied aneroids  are  employed  speedily  after  that  date,  and  again  experience 
reductions  in  pressure  of  tlie  same  amount,  and  for  the  same  length  of  time  as 
during  the  examination,  it  may  be  useful  to  pay  attention  to  the  errors  which 
can  be  deduced  from  the  certificates.  A  single  week,  however,  of  active  use 
(that  is  to  say,  of  considerable  variations  in  pressure)  may  considerably  alter 
the  index-errors,  and  will  certainly  change  them  to  an  appreciable  extent, 
while  under  more  prolonged  use  further  variations  will  most  likely  occur. 

It  seems  to  me,  therefore,  indispensable  for  all  those  who  aim  at  correct 
measurement  of  altitude  above  the  level  of  the  sea,  by  means  of  aneroids,  and 
especially  for  those  engaged  upon  prolonged  journeys,  to  be  at  all  times  able  to 
determine  their  index-errors. 

§  50.  I  now  draw  attention  to  a  feature  in  the  working  of  aneroids  which 
has  as  yet  only  been  casually  referred  to  in  this  paper,  namely,  the  want  of 
correspondence  between  differences  of  pressure  indicated  by  them  in  ascending 
and  in  descending  observations.  Under  certain  conditions  descending  readings 
indicate  less  difference  of  pressure  than  ascending  ones,  and  under  other  con- 
ditions the  reverse  may  be  the  case.  These  facts  can  be  utilized  in  deter- 

1  The  index-errors  stated  in  Col.   2  of  the  table  upon  p.  38,  with  the  exception 
of  F  (Hicks),  580  and  1021  (Casella),  and  170  (Cooke),  were  all  acquired  in  the  course 
of  the  experiments  which  are  described  in  Part  2.     One  of  them,  it  will  be  seen,  is  as 
much  as  +0*478,  and  another  -0*407  of  an  inch.     These  alterations  occurred  though 
the  instruments  were  used  with  the  utmost  tenderness.     Under  the  rougher  usage  to 
which  they  would  necessarily  be  submitted  in  the  field  there  would  be  liability  to  still 
greater  changes. 

2  In  their  present  form.     See  pp.  51-54. 


IN  DETERMINATION  OF  ALTITUDES.  41 

mination  of  altitudes.  I  shall  presently  endeavour  to  show  experimentally 
the  effect  which  is  produced  by  the  intervention  of  a  greater  or  less  space  of 
time  ;  but,  before  doing  so,  I  will  restate  a  few  of  my  facts  in  a  somewhat 
different  manner. 

§  51.  All  aneroids  commence  to  lose  upon  the  mercurial  barometer 
directly  pressure  is  reduced.  They  lose  a  certain  amount  if  pressure  is 
reduced  to  the  extent  of  an  inch,  they  lose  a  larger  amount  if  it  is  reduced 
2  inches,  and  more  and  more  for  each  successive  inch.  Also  the  loss  is 
greater  in  a  day  than  it  is  in  an  hour,  greater  in  a  week  than  it  is  in  a  day, 
and  it  continues  to  augment  perceptibly  for  about  a  month.  Further, 
immediately  pressure  commences  to  be  restored,  an  aneroid  endeavours  to 
recover  the  previous  loss.  This  latter  tendency  is  more  and  more  important 
as  each  inch  of  pressure  is  restored,  and  after  return  to  normal  pressure  it 
continues  to  operate  (though  with  constantly  diminishing  force)  for  several 
weeks. 

§  52.  It  must  therefore  be  apparent  that  the  difference  of  pressure  (or 
difference  of  level)  which  will  be  indicated  by  an  aneroid  between  any  two 
stations  will  be  influenced  by  the  greater  or  less  amount  of  time  which  may 
intervene  between  the  readings  at  the  two  stations.  In  the  case  of  a  moun- 
tain 5000  feet  high  (or  any  other  height)  one  result  will  be  attained  from  an 
aneroid  if  there  is  an  interval  of  four  hours  between  a  reading  at  the  bottom 
and  another  at  the  top,  a  different  result  will  be  attained  if  there  is  an 
interval  of  twelve  hours,  and  yet  another  if  there  is  an  interval  of  twenty- 
four  hours  ;  and  the  difference  of  pressure  (or  the  altitude)  which  will  be 
indicated  will  be  greater  in  the  second  case  than  in  the  first,  and  greater  still 
in  the  third  than  in  the  second.  It  will  not,  perhaps,  be  so  readily  apparent 
why  descending  readings,  closely  following  upon  ascending  ones,  always  differ 
from  them,  and  I  will  state  three  imaginary  cases  in  which  this  will  occur. 

§  53.  Let  us  imagine  the  case  of  an  ascent  being  made  in  five  hours,  of  a 
mountain  having  a  pressure  of  25  inches  reigning  at  its  top  and  a  pressure 
of  30  inches  at  its  base.  The  diminution  in  pressure  which  will  occur  during 
the  ascent  will  be  gradual,  and  the  effect  which  will  be  produced  on  the 
aneroid  by  the  time  it  arrives  at  the  summit  will  be  much  less  than  the 
effect  which  would  have  been  produced  upon  it  if  it  had  sustained  a  constant 
diminution  in  pressure  of  5  inches  for  five  consecutive  hours.  The  loss 
upon  the  mercurial  barometer  will  nevertheless  be  well  marked,  and  at 
the  end  of  the  fifth  hour,  as  the  aneroid  will  then  experience  a  constant 
reduction  in  pressure  of  5  inches,  it  will  lose  rapidly.  If  a  reading  is 
taken  on  the  summit  immediately  upon  arrival  there,  the  altitude  ob- 
served by  inspection  of  the  aneroid  will  be  somewhat  (but  not  much) 
greater  than  the  truth,1  and  it  will  be  less  than  the  altitude  which  will 
be  observed  if  another  reading  is  taken,  an  hour  later.  The  result  in 

1  It  is  of  course  assumed  that  the  aneroid  has  been  correctly  graduated,  to  read 
instantaneously  against  the  mercurial  barometer ;  and  it  is  also  assumed  that  there  is  no 
change  in  atmospheric  pressure,  within  the  period  involved,  either  at  the  higher  or 
lower  station. 

G 


42  UPON  THE  USE  OF  THE  ANEROID  BAROMETER 

each  case  is  due  to  the  tendency  to  lose  upon  the  mercurial  barometer, 
— which  will  still  be  actively  at  work  at  the  end  of  the  sixth  hour,  and 
at  the  end  of  that  time  let  us  suppose  the  descent  is  commenced. 

Immediately  the  descent  is  commenced  pressure  begins  to  be  restored. 
The  tendency  to  lose  still  continues,  though  with  constantly  diminishing 
force.  For  it  is  less  potent  at  a  pressure  of  26  inches  than  it  was  upon 
the  summit  at  a  pressure  of  25  inches,  less  potent  still  at  27  inches, 
and  it  dies  out  on  return  to  normal  pressure.  But  the  moment  pressure 
begins  to  be  restored  (as  it  does  directly  the  descent  commences)  the 
tendency  to  recover  sets  in.  This  is  feeble  at  first  (when  the  restoration 
in  pressure  is  slight)  and  it  becomes  stronger  and  stronger  as  normal 
pressure  is  approached.  Thus,  during  the  descent,  there  are  two  tendencies 
at  work — the  tendency  to  lose  in  consequence  of  diminution  in  pressure, 
and  to  recover  in  consequence  of  restoration  of  pressure.  These  counter- 
act each  other,  and  the  effect  is  the  recovery  is  retarded.  I  have  found 
experimentally  that,  through  the  tendency  to  recover,  a  greater  difference 
of  pressure  (or  greater  altitude)  than  the  truth  would  always  be  obtained 
from  descending  observations  (following  ascending  ones)  if  this  were  not 
checked  by  the  tendency  to  lose ;  and  I  have  also  found  experimentally 
that  retardation  of  the  recovery  causes  descending  readings  to  indicate 
less  difference  of  pressure  than  ascending  ones.1 

§  54.  In  Case  2,  let  us  suppose  the  same  mountain  is  ascended  again, 
at  the  same  rate,  and  that  the  traveller  remains  an  entire  day  on  the 
summit.  In  this  case,  if  the  traveller  reads  his  aneroid  immediately 
upon  arrival  at  the  summit  he  will,  as  before,  obtain  an  altitude  which 
will  be  somewhat  greater  than  the  truth  ;  and  should  he  read  it  again  at 
the  expiration  of  twenty-four  hours  he  will  obtain  an  altitude  consider- 
ably higher  than  he  did  from  his  second  reading  upon  his  first  ascent, 
inasmuch  as  the  aneroid  will  have  been  subjected  continuously  to  a 
diminution  in  pressure  of  5  inches  for  an  entire  day  (instead  of  a  single 
hour),  and  will  have  been  losing  upon  the  mercurial  barometer  during 
the  whole  time.  At  the  end  of  this  time,  the  tendency  to  lose  will  have 
become  much  less  active  (see  table  on  p.  27) ;  and,  should  he  now  com- 
mence to  descend,  the  tendency  of  the  aneroid  to  recover  will  be  less 
checked  than  before.  In  consequence  of  this,  over  precisely  the  same 
ground,  even  if  he  comes  down  at  precisely  the  same  rate  as  upon 
his  first  descent,  his  descending  readings  will  yield  a  result  differing 
from  that  obtained  011  his  first  descent,  and  will  indicate  a  greater  differ- 
ence of  pressure,  and  greater  difference  of  level  between  the  summit  and 
the  base  than  upon  the  first  occasion. 

§  55.  For  Case  3,  let  us  suppose  the  same  mountain  is  ascended  again, 
at  the  same  rate  as  before,  and  that  the  traveller  remains  an  entire  month  on 

1  Not,  however,  necessarily  less  than  the  truth.  See  later.  Sometimes  the  opposition 
of  these  tendencies  produces  a  perfect  correction  ;  and  the  aneroid,  at  one  point  of 
its  scale,  will  indicate  the  same  differences  as  the  mercurial  barometer.  See  the 
Kew  certificate  given  on  p.  51. 


IN  DETERMINATION  OF  ALTITUDES.  43 

the  summit.  At  the  end  of  this  time  the  tendency  to  lose  will  have  ceased 
(or  will  be  exerted  very  feebly).  Thus,  when  the  descent  is  commenced, 
the  tendency  to  recover  will  be  unretarded  ;  and,  in  consequence  of  this, 
over  precisely  the  same  ground,  and  during  the  same  lapse  of  time  as  before, 
the  descending  readings  will  yield  a  result  which  will  differ  from  those 
obtained  upon  the  first  two  descents,  and  will  indicate  a  greater  difference  of 
pressure,  and  greater  difference  of  level  than  upon  the  first  two  occasions.1 

§  56.  The  remarks  which  have  been  made  upon  pp.  41-2  will  probably  be 
better  apprehended  after  the  tables  have  been  examined  that  accompany  the 
following  experiments.  These  two  experiments  are  designed  to  show  that,  in 
measuring  precisely  the  same  amount  of  difference  of  pressure  upon  several 
occasions,  aneroids  will  yield  dissimilar  results  upon  each  occasion,  if  the  time 
conditions  are  dissimilar  ;  and  also  to  exhibit  the  manner  in  which  exact 
knowledge  of  the  behaviour  of  aneroids  may  be  turned  to  account  in  the 
measurement  of  pressures,  and  through  them  of  altitudes. 

§  57.  EXAMPLE  1.  The  case  is  supposed  of  a  traveller,  provided  with 
aneroids,  starting  from  the  level  of  the  sea  to  ascend  a  mountain — the 
height  of  which  is  unknown.  It  is  supposed  that  no  change  in  atmospheric 
pressure  occurs  during  the  expedition,  and  that  the  traveller  proposes  to 
deduce  the  altitude  of  his  mountain  from  means  of  ascending  and  descend- 
ing observations  of  the  differences  of  pressure  indicated  by  his  aneroids. 

He  is  supposed  to  occupy  four  hours  upon  the  ascent ;  to  remain  one  hour 
upon  the  top  ;  and  to  descend  from  the  summit  to  his  starting-point  (at  the 
level  of  the  sea)  in  two  hours  more.  To  read  his  aneroids  just  before  his 
departure  from  the  level  of  the  sea  ;  upon  the  summit,  one  hour  after  his 
arrival  there ;  at  the  level  of  the  sea  immediately  upon  his  return,  and  again 
at  the  level  of  the  sea  twenty-two  hours  later.  What  error,  expressed  in 
barometric  inches,  is  he  likely  to  fall  into  from  his  employment  of  aneroids 
in  this  manner  ? 

For  this  experiment  I  used  twelve  aneroids,  all  of  the  watch  size.2  The 
aneroids  were  read ;  pressure  was  then  reduced  gradually  for  four  successive 
hours,  at  the  rate  1-146  inches  per  hour  ;  it  was  maintained  at  25*061  inches 
for  one  hour,  and  the  aneroids  were  again  read  at  the  expiration  of  this  (the 
fifth)  hour.  Pressure  was  then  gradually  restored  during  two  hours.  By  the 
end  of  that  time  the  aneroids  arrived  again  at  the  pressure  from  which  they 

1  It   is  scarcely  necessary  to  say  that  should  an  aneroid  be  used  for  ascending 
observations,  immediately  (or  shortly)  after  it  has  experienced  augmentation  of  pressure, 
the   tendency   to   recover   will    retard   the    tendency   to   lose   in   precisely   the    same 
manner  as  the  tendency  to   lose  retarded  the  tendency  to  recover  in  the  instances 
imagined  in  §§  53-55.     Thus,  if  a  traveller  ascends  a  mountain  upon  two  successive 
days,  using  the  same  aneroids  on  each  occasion,  and  starts  upon  his  second  ascent  (say) 
ten  hours  after  his  return  to  camp  from  the  first  one,  he  will  from  his  second  set  of 
ascending  readings  obtain  a  less   difference  of  pressure,   and  a  smaller  difference  of 
level,  than  he  did  upon  his  first  ascent. 

It  may  be  pointed  out  here  that  the  embarrassment  caused  by  the  '  recovery '  has 
greatly  protracted  these  investigations.  In  the  case  of  repetitions,  it  has  sometimes 
been  necessary  to  put  instruments  aside  for  months. 

2  Because  this  is  the  size  most  commonly  used  by  travellers. 


44  UPON  THE  USE  OF  THE  ANEROID  BAROMETER 


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IN  DETERMINATION  OF  ALTITUDES.  45 

had  started,  namely,  29-645  inches.  The  instruments  were  then  again  read, 
and  were  again  read  twenty-two  hours  later. 

In  Col.  1  of  the  annexed  table,  the  readings  are  given  which  were 
taken  at  the  assumed  sea-level ;  in  Col.  2,  the  readings  upon  the  supposed 
summit,  one  hour  after  arrival  ;  in  Col.  4,  the  readings  immediately  upon 
return  to  the  starting-point ;  and,  in  Col.  6,  the  readings  which  were  taken 
twenty -two  hours  later.  In  Col.  3  the  differences  are  given  between  the 
readings  in  Cols.  1  and  2  ;  in  Col.  5,  the  differences  between  the  readings 
in  Cols.  2  and  4  ;  and  in  Col.  7,  the  differences  between  the  readings  in 
Cols.  2  and  6.  At  the  bottom  of  the  table  I  give  the  "  Means  of  the  Ane- 
roids," and  the  differences  of  those  means  from  the  difference  of  pressure 
indicated  by  the  mercurial  barometer. 

For  the  present,  I  invite  attention  only  to  the  means  of  the  aneroid 
observations  in  Columns  3,  5,  and  7.  The  first  will  be  found  to  be  0'021  of 
an  inch  in  excess  of,  the  second  to  be  0*030  of  an  inch  less  than,  and  the 
third  to  be  0*012  of  an  inch  in  excess  of  the  difference  of  pressure  indicated 
by  the  mercurial  barometer. 

§  58.  EXAMPLE  2.  It  is  supposed  that  our  traveller's  observations  were 
considered  unsatisfactory  ;  that  it  was  said  his  work  was  too  hurriedly  per- 
formed, and  that  he  should  have  taken  at  least  two  readings  upon  the  sum- 
mit, several  hours  apart,  and  should  have  used  the  means  of  these  two 
readings. 

He  is  supposed  to  have  made  another  expedition ;  to  have  started  on  the 
first  day  at  10  a.m.,  and  to  have  reached  the  summit  at  5  p.m.  ;  to  have 
remained  there  until  5  p.m.  on  the  second  day ;  and  then,  as  before,  to  have 
descended  in  two  hours  to  the  level  of  the  sea.  He  is  supposed  to  have 
read  his  aneroids  just  before  departure  from  the  level  of  the  sea ;  to  have 
read  them  again  at  1 1  a.m.  and  at  5  p.m.  on  the  day  which  was  passed  on 
the  summit ;  and  again  immediately  on  return  to  the  level  of  the  sea. 
What  superiority  would  these  observations  possess  over  the  former  ones  ? 

In  this  experiment  I  used  the  same  aneroids  as  before,  and  read  them 
against  the  mercurial  barometer  at  the  hours  mentioned  above.  During  the 
seven  hours  which  are  supposed  to  have  been  occupied  by  the  ascent,  press- 
ure was  reduced  at  the  rate  of  0' 65 5  of  an  inch  per  hour,  and  during  the 
descent  it  was  restored  gradually. 

In  Col.  1  of  the  table  (Example  2)  the  readings  are  given  which  were 
taken  at  the  assumed  sea-level ;  in  Col.  2  the  readings  on  the  supposed  sum- 
mit, eighteen  hours  after  arrival ;  in  Col.  4  the  readings  on  the  supposed 
summit  twenty-four  hours  after  arrival ;  and  in  Col.  6  the  readings  upon 
return  to  the  starting-point.  In  Col.  3  the  differences  are  given  between 
the  readings  in  Cols.  1  and  2  ;  in  Col.  5  the  differences  between  Cols.  1  and 
4;  and  in  Col.  7  the  differences  between  Cols.  4  and  6.  I  again  ask 
attention  first  of  all  to  be  given  to  the  means  of  the  aneroid  observations  in 
Columns  3,  5,  and  7.  The  first  will  be  found  to  be  O'lll,  the  second  to 
be  0-134,  and  the  third  to  be  0-073  of  an  inch  in  excess  of  the  true  differ- 
ence of  pressure  observed  from  the  mercurial  barometer. 


46  UPON  THE  USE  OF  THE  ANEROID  BAROMETER 


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IN  DETERMINATION  OF  ALTITUDES.  47 

§  59.  "We  have  thus  obtained  six  different  results  in  the  measurement 
of  a  difference  of  pressure  of  4*584  inches.  One  is  0*030  of  an  inch  less 
than  the  truth,  and  the  others  are  0*012,  0*021,  0-073,  0-111,  and  0*134 
of  an  inch  greater  than  the  truth.  Some  may  say  "  this  is  another  instance 
of  the  uncertainty  of  aneroids."  Internal  examination  of  these  readings 
will,  however,  show  that  aneroids  work  with  great  certainty,  and  follow 
rules  which  can  be  defined  with  some  precision.  Let  us  first  examine 
the  ascending  readings. 

After  having  had  pressure  reduced  gradually  in  four  hours  to  the  extent 
of  4*584  inches,  and  after  being  kept  at  that  pressure  for  one  hour,  the 
mean  of  the  twelve  aneroids  indicated  a  fall  in  pressure  0*021  of  an  inch 
more  than  the  truth. 

After  having  had  pressure  reduced  gradually  in  seven  hours  to  the 
extent  of  4*584  inches,  and  after  being  kept  at  that  pressure  for  eighteen 
hours,  the  mean  of  the  twelve  aneroids  indicated  a  fall  in  pressure  0*111 
of  an  inch  more  than  the  truth. 

After  being  kept  at  this  reduction  of  pressure  for  six  hours  more,  the 
mean  of  the  twelve  aneroids  indicated  a  fall  in  pressure  0*134  more  than 
the  truth. 

This  behaviour  is  consistent  with  the  rule  which  has  been  already 
stated,  namely,  that  all  aneroids  lose  upon  the  mercurial  barometer  upon 
being  submitted  to  diminished  pressure,  and  that  the  extent  of  the  loss  in 
any  operation  will  depend  upon  the  lapse  of  time  as  well  as  upon  the  extent 
of  the  diminution  in  pressure. 

The  behaviour  of  the  individual  instruments  in  these  experiments  will 
also  be  found  consistent.  If  Col.  3  of  tab.  Example  1  is  compared  with 
Col.  3  of  tab.  Ex.  2,  it  will  be  found  that  every  single  instrument  in  the 
latter  column  indicated  a  greater  fall  than  in  the  former  *  and  if  Cols.  3 
and  5  of  tab.  Ex.  2  are  compared,  it  will  be  found  that  the  six  additional 
hours  upon  the  supposed  summit  produced  a  distinct  increase  in  the  loss 
upon  the  mercurial  in  eleven  out  of  the  twelve  instruments.1 

§  60.  Turning  now  to  the  means  of  the  descending  readings  we  find 
the  first  giving  a  result  0*030  of  an  inch  less  than  the  truth,  and  the 
others  0*012  and  0*073  of  an  inch  more  than  the  truth.  The  time  con- 
ditions were  different  in  each  of  these  cases,  and  in  this  fact  I  seek  for 
an  explanation. 

The  first  of  these  means  (  —  0*030)  is  derived  from  the  readings  of 
twelve  aneroids,  which  in  four  hours  had  pressure  reduced  to  the  extent 
of  4*584  inches,  were  then  kept  at  that  pressure  for  one  hour,  and  then 
had  pressure  restored  gradually  during  two  hours.  The  resulting  mean 
is  consistent  with  the  general  behaviour  of  aneroids.  It  is  the  rule  that 

1  The  reading  of  aneroid  30  in  Col.  4  of  tab.  Ex.  2  is  marked  'discordant.' 
When  an  aneroid  is  under  the  receiver  of  an  air-pump,  it  is  not  always  possible 
to  assist  the  movements  of  the  index-needle  by  tapping.  The  discrepancy  between 
the  two  readings  of  No.  30  may  have  occurred  through  some  slight  impediment  which 
would  have  been  immediately  overcome  if  the  instrument  could  have  been  tapped  in 
the  usual  way. 


48  UPON  THE  USE  OF  THE  ANEROID  BAROMETER 

all  descending  observations  of  aneroid  barometer  which  follow  ascending  ones 
indicate  less  increase  in  pressure  than  the  truth  if  they  are  made  quickly  (ie. 
if  only  a  short  time  elapses  between  the  readings  at  the  higher  and  the  lower 
station),  provided  also  that  the  ascending  observations  have  been  made  quickly 
(that  is,  that  only  a  short  time  has  elapsed  between  the  readings  at  the  lower 
and  the  upper  station).1 

The  second  of  the  means  of  the  descending  observations  (  +  0*012)  is 
derived  from  readings  of  the  same  aneroids,  twenty-two  hours  after  they 
had  returned  to  normal  pressure,  and  is  consistent  with  the  general  be- 
haviour of  aneroids.  The  rule  is  that  all  aneroids  without  exception  lose 
upon  the  mercurial  barometer  when  submitted  to  diminished  pressure,  and  re- 
cover a  portion  of  the  previous  loss  when  pressure  is  restored.2  In  this  in- 
stance they  recovered  0-042  of  an  inch  (the  difference  between  -0-030 
and  +0'012)  in  twenty-two  hours. 

The  third  of  the  means  of  the  descending  observations  (  +  0*073)  is 
derived  from  the  readings  of  the  same  aneroids  after  they  had  experi- 
enced reduction  of  pressure  to  the  extent  of  4 '58 4  inches  in  seven  hours, 
and  had  then  been  kept  continuously  at  that  pressure  for  twenty -four 
hours.  At  the  end  of  that  time  they  had  pressure  restored,  as  before,  in 
the  course  of  two  hours.  The  result  is  not  discordant  although  it  differs 
from  the  others.  The  instruments  experienced  reduction  of  pressure  for 
a  greater  length  of  time  than  before,  and  consequently  lost  more  than 
before.  At  the  end  of  twenty-four  hours  the  tendency  to  lose  was  much 
less  active  than  it  was  on  the  first  occasion  (at  the  end  of  one  hour). 
The  increase  in  the  difference  of  pressure  that  they  indicated  (namely 
4 '65 7  inches,  as  compared  with  4*554  and  4' 595)  was  due  to  there 
being  a  larger  amount  to  recover,  and  to  the  recovery  being  less  retarded 
than  before  by  the  tendency  to  lose  (see  §§  53-5). 

The  behaviour  of  the  individual  instruments  is  consistent  in  the 
descending  readings.  If  Cols.  5  and  7  of  tab.  Ex.  1  are  compared,  it 
will  be  seen  that  every  single  instrument  indicated  a  greater  difference  of 
pressure  in  the  latter  than  in  the  former;  and  the  same  will  again  be 
found  if  Col.  7  of  tab.  Ex.  1  is  compared  with  Col.  7  of  tab.  Ex.  2. 

§  61.  If  the  means  of  the  aneroids  are  now  examined  to  see  what 
combination  gives  the  closest  approximation  to  the  mercurial  barometer, 
it  will  be  found  that  the  best  result  is  obtained  by  taking  the  mean  of 
the  means  of  Columns  3  and  5,  in  Example  1. 

Mean  of  fall  in  pressure  indicated  by  aneroids  (Col.  3)    .       .  4*6050  inches. 

do.         rise  do.  do.      (CoL  5)    .       .4*5540       „ 

Mean  of  the  rise  and  fall  in  pressure  indicated  by  aneroids     .4*5795       „ 

do.  do.  do.         .  Merc.  Bar.     4*5840       „ 

Error  of  the  aneroids,    -  0*0045  of  an  inch. 

1  See  §  53,  and  the  Kew  certificate  upon  p,  51. 

2  See  §  35,  p.  31,  of  this  paper. 


IN  DETERMINATION  OF  ALTITUDES.  49 

It  will  be  found  that  no  result  so  accurate  can  be  obtained  from  any 
combination  of  the  means  in  Example  2,  and  that  the  inferiority  of  the  latter 
is  distinctly  traceable  to  the  greater  lapse  of  time  between  the  observations. 

It  is  possible,  therefore,  if  aneroids  are  used  in  this  way,  in  measure- 
ment of  a  difference  of  level  involving  a  difference  of  pressure  of  4-584 
inches  to  get  a  result  only  0*0045  of  an  inch  from  the  truth.  Critics 
may  say  that  this  close  result  is  entirely  accidental ;  or  that  no  traveller 
would  employ  twelve  aneroids  upon  such  an  expedition  ;  or  that  one 
would  be  as  likely  to  be  provided  with  several  of  the  worst  as  with 
several  of  the  best  of  the  dozen  which  were  used  in  the  experiments. 
Let  us  therefore  examine  some  of  the  results  separately. 

The  aneroid  which  yielded  the  worst  result  was  No.  33. 
No.  33,  ascending  observation,  4-520^1  ,r 

do.     descending          do.      '  4.472JMean  4-4960. 

The  two  aneroids  which  yielded  the  worst  combined  mean  result  were 

Nos.  32  and  33. 

No.  32,  ascending  observation,  4-5501 
do.      descending         do.         4-482  ' 
No.  33,  ascending          do.        4-520  \  Mean  4'506(X 
do.     descending         do.         4-472J 

The  two  aneroids  with  the  largest  initial  index-errors  were  Nos.  29  (  —  0'495) 

and  40  (  +  0-505). 

No.  29,  ascending  observation,  4*6001 

do.     descending         do.         4-542  ! 

No.  40,  ascending  do.         4-590  [ 

do.     descending         do.         4*537  j 

The  aneroid  which  gave  the  best  result  was  No.  30. 

No.  30,  ascending  observation,  4*605^  ,.- 

,.&  ,  _  >-Mean  4-5885. 

do.     descending         do.         4-572,' 

Error  of  aneroid  No.  30,    +  0-0045  of  an  inch. 

Thus,  the  worst  result  which  was  yielded  by  any  single  aneroid  was 
less  than  two  per  cent  in  error,  and  the  best  one  (like  the  mean  of  the 
whole)  differed  only  0*0045  of  an  inch  from  the  mercurial  barometer. 

Twelve  aneroids  and  no  more  were  employed  in  this  experiment,  and 
none  of  these  were  specially  selected  for  it.  They  came  from  the  stock  of 
Mr.  Hicks,  and  the  maker  was  unaware  of  the  nature  of  the  tests  to  which 
they  would  be  put.  At  the  commencement  of  the  experiment,  care  was 
taken  that  they  were  in — what  I  have  ventured  to  term — "a  state  of  repose," 
and  no  such  results  could  have  been  obtained  if  this  had  been  neglected. 

The  reader  will  by  this  time  perceive  that  not  only  are  there  various 
ways  in  which  aneroids  can  be  used  but  that  the  precise  manner  in  which 
they  can  be  most  advantageously  employed  will  be  determined  by  the 
necessities  of  the  case,  I  have  first  set  before  him  some  of  the  principal 

H 


50  UPON  THE  USE  OF  THE  ANEROID  BAROMETER 

causes  of  error,  and  have  then  endeavoured  to  point  out  some  ways  in 
which  these  can  be  guarded  against.  He  has  seen  that  precautions  are 
desirable  in  some  instances,  and  are  indispensable  in  others.  He  has  seen 
that  aneroids  are  at  present  constructed  to  read  instantaneously,  or  nearly 
so,  against  the  mercurial  barometer,  and  he  has  been  shown  that  they  are 
very  materially  affected  by  variations  in  pressure,  that  the  extent  to  which 
they  are  affected  depends  upon  the  greater  or  less  lapse  of  time,  and  that 
they  are  unequally  affected  by  these  causes. 

§  62.  Some  may  wish  to  measure  a  mound  in  a  few  minutes  or 
to  bound  in  balloon  ten  thousand  feet  in  an  hour,  and  others  to  spend 
a  day  upon  the  ascent  of  a  mountain  or  to  pass  weeks,  months,  or  years 
at  great  elevations  in  the  interior  of  continents.  It  is  impossible  to 
dictate  the  right  course  of  procedure  for  every  case  that  may  occur. 
The  best  results  will  be  attained  by  those  who  make  themselves 
acquainted  with  the  rules  that  govern  aneroids  in  general,  and  with  the 
particular  behaviour  of  the  instruments  which  may  be  employed.  I  offer 
the  following  remarks  as  hints  rather  than  as  directions. 

1.  When  only  a  few  minutes  elapse  between  readings,  such  errors  as 
may  occur  will  most  likely  be  due  to  errors  of  graduation. 

2.  When   readings   are   taken   a    few   hours    apart   (for   difference   of 
level)  it  will  be  advantageous  to   employ   the   means   of  ascending   and 
descending  readings  (§§  52,  61). 

3.  When  days  elapse  between   readings  taken  to  obtain  difference  of 
level,  it  will  be  necessary  to  know  the  amounts  which  will  probably  be 
lose  or  recovered  at  the  pressures  experienced,  during  the  length  of  time 
concerned  ;  and  desirable  to  be  able  to  determine  index-errors  (§  47). 

4.  It  seems   to    me   indispensable   for   all    those   who   aim    at    correct 
measurement  of  altitudes  above  the  level  of  the  sea  by  means  of  aneroids 
to  be  at  all  times  able  to  determine  their  index-errors. 

No  one,  I  think,  will  regret  paying  attention  to  the  following  recom- 
mendations : — 1.  Prefer  open  scales.  2.  Prefer  aneroids  of  large  diameter 
to  the  watch  size.  3.  Prefer  aneroids  which  have  been  made  some  length 
of  time.1  4.  Avoid  working  aneroids  up  to  the  extreme  inferior  limit 
of  their  scales.  5.  Treat  an  aneroid  with  the  same  care  as  a  watch. 
6.  Trust  more  to  the  scale  of  inches  than  to  the  scale  of  feet. 

Something  may  be  gained  by  paying  attention  to  the  foregoing  hints 
and  recommendations,  but  the  two  essential  requirements  for  those  who 
use  aneroids  in  the  field  upon  prolonged  journeys  are  1.  knowledge  of 
the  amounts  which  will  probably  be  lost  and  recovered  by  their  instru- 
ments, and  2.  ability  to  determine  their  index -errors  at  any  time. 

§  63.  I  do  not  venture  to  suggest  what  form  of  certificate  would  be 
best  adapted  for  general  use.  The  settlement  of  this  may  well  be  left 

1  Old  aneroids  (that  is,  aneroids  which  have  been  made  for  a  number  of  years) 
are  generally  more  sober  and  regular  in  their  conduct  than  young  ones.  This  fact 
is,  I  believe,  already  well  known  to  instrument  makers. 


IN  DETERMINATION  OF  ALTITUDES. 
CERTIFICATE    OP   EXAMINATION 


51 


ISSUED  BY 


THE     KEW    OBSERVATORY, 

RICHMOND,  SURREY. 


ANEROID    BAROMETER    No.   899. 

by  CART,  London. 

Compared  with  the  Standard  Barometer  of  the  Kew  Observatory 
(reduced  to  32°  JW-)  with  the  following  results. 


Pressure- 


XV 


/f 


Correction  to 
Aneroid  with  a 

pressure 
diminishing. 


f*   00 


0  '. 


0-00 

0  •  06 


Correction  to 
Aneroid  with  a 

pressure 
increasing. 


-A*. 


-t~0  3* 
-+0.30 


+0 


i.  30 

i 

+0. 


*  It  is  probable  that  this  correction  will  have  become  reduced  to  that  first 
obtained  after  the  instrument  has  remained  at  the  normal  atmospheric  pressure  for 
a  short  time. 

Note. — When  the  sign  of  the  Correction  is  +,  the  quantity  is  to  be  added  to  the 
observed  scale  reading,  and  when  -  to  be  subtracted  from  it. 


KEW  OBSERVATORY,  October  1888. 


G.  M.  WHIPPLE, 

SUPERINTENDENT. 


52  UPON  THE  USE  OF  THE  ANEROID  BAROMETER 

to  those  whose  business  it  is  to  attend  to  such  matters  ;  but,  whatever 
it  may  be,  it  should,  I  think,  very  materially  differ  from  the  certificate 
given  overleaf,  which  is  one  recently  issued  by  Kew  Observatory.  It  is 
convenient  to  refer  to  this  certificate  for  illustration  of  several  of  the 
points  which  have  been  touched  upon. 

The  aneroid  No.  899,  Gary,  has  twice  passed  through  my  hands — 
on  the  first  occasion  in  1889,  seven  months  after  it  had  been  tested  at 
Kew,  and  on  the  second  in  1890,  after  a  journey  in  the  Caucasus  upon 
which  it  had  been  employed.  In  1889,  when  it  first  came  to  me, 
I  tested  it  under  the  air-pump  in  the  ordinary  manner,  reducing  press- 
ure inch  by  inch,  and  reading  it  against  the  attached  mercurial  baro- 
meter at  each  successive  inch.1  The  time  occupied  in  reducing  it  from 
30  to  15  inches  amounted  to  twenty -five  minutes.  The  results  of 
my  comparisons  agreed  closely,  at  every  inch  of  the  scale,  with  those 
obtained  at  Kew.  At  29  inches  I  found  the  aneroid  read  0-073  of  an 
inch  too  high  (the  corresponding  result  at  Kew  was  +0'050),  and  at 
15  inches  it  read  0'045  too  low  (Kew  result  -0-050).  As  the  Kew 
certificate  only  goes  to  the  nearest  half-tenth  of  an  inch,  their  results 
and  mine  may  be  considered  to  agree,  and  to  be  satisfactory,  as  they 
show  that  No.  899,  Gary,  upon  being  tested  independently  upon  two 
occasions,  seven  months  apart,  behaved  almost  alike  on  the  two  occasions, 
and  that  the  prognostication  contained  in  the  passage  at  the  foot  of  the 
Kew  certificate  was  correct.2 

I  then  reduced  No.  899,  Gary,  to  a  pressure  of  16  inches,  and 
kept  it  at  that  pressure  for  eleven  days.  At  the  end  of  a  week  this 
aneroid  lost  0*625  of  an  inch,  and  at  the  end  of  the  eleventh  day 
0-736  of  an  inch  upon  the  mercurial  barometer  (the  Kew  result  was 
0*050).  Thus,  if  the  owner  of  this  aneroid  had  remained  with  it  at  a 
pressure  of  16  inches  for  a  week,  and  had  employed  the  correction 
stated  upon  the  Kew  certificate,  he  would  probably  have  under-estimated 
the  pressure  to  the  extent  of  0-575  of  an  inch,  which  would  have 
introduced  a  very  large  error  into  computations  of  altitude.  He  would 
have  employed  the  error  due  to  a  diminution  of  pressure  for  the  space 
of  about  twenty-five  minutes  instead  of  that  arising  in  a  week,  and  from 
this,  I  think,  it  sufficiently  appears  that  it  is  desirable  to  present  certifi- 
cates of  examination  in  a  form  different  from  that  which  is  given  upon 
p.  51. 

§  64.  The  readings  of  No.  899,  Gary,  which  were  taken  during  the  Kew 
examination  can  be  recovered  by  applying  the  corrections  stated  upon  the 
certificate,  and  are  given  below.  In  Col.  1  we  have  the  readings  of  the  Kew 
Standard  Barometer,  in  Col.  2  the  simultaneous  readings  of  the  aneroid  as 
pressure  was  reduced  inch  by  inch,  and  in  Col.  3  the  simultaneous  readings 
of  the  aneroid  as  pressure  was  restored  inch  by  inch. 

1  The  mercurial  barometer  readings,  for  comparison,  were  reduced  to  32°  Faht. 

2  This  passage  (marked  by  an  asterisk)  is  a  recognition  of  "  the  recovery. " 


DETERMINATION  OF  ALTITUDES. 


53 


1. 

2. 

3. 

Readings 
of  K.  O.  Standard 
Barometer. 

Readings 
of  No.  899,  Gary, 
with  pressure 
diminishing. 

Readings 
of  No.  899,  Gary, 
with  pressure 
increasing. 

inches. 

inches. 

inches. 

30-000 

30-000 

29-800 

29-000 

29-050 

28-750 

28-000 

28-050 

27-800 

27-000 

27-000 

26-750 

26-000 

26-000 

25-700 

25-000 

25-050 

24-700 

24-000 

24-050 

23-700 

23-000 

23-000 

22-650 

22-000 

22-000 

21-650 

21-000 

21-000 

20-650 

20-000 

19-950 

19-650 

19-000 

18-950 

18-700 

18-000 

17-950 

17-750 

17-000 

16-950 

16-800 

16-000 

15-950 

15-850 

15-000 

14-950 

14-900 

It  will  be  seen  that  at  no  single  inch  do  the  aneroid  readings  in 
the  two  columns  agree.  Every  reading  in  Col.  3  is  lower  than  the 
corresponding  one  in  Col.  2.  It  is  apparent  that  in  the  short  space  of 
time  during  which  this  aneroid  was  submitted  to  diminished  pressure 
(a  space  of  time  which  probably  did  not  amount  to  one  hour  in  all), 
it  showed  a  distinct  loss  upon  the  mercurial  barometer  at  every  inch  of 
its  scale.  The  differences  between  the  readings  in  the  two  columns  at  each 
inch  represent  the  amounts  lost  at  those  parts  of  the  scale  during  the  brief 
time  that  was  occupied  in  reducing  pressure  to  15  inches  and  restoring  it 
again.  Thus,  at  21  inches,  although  there  is  no  error  in  Col.  2  (the 
aneroid  reading  truly  against  the  mercurial  barometer)  there  is  a  minus 
error  of  0-350  of  an  inch  in  Col.  3.  This  amount  (0-350  of  an  inch) 
is  the  amount  which  was  lost  during  the  time  pressure  was  reduced 
inch  by  inch  from  21  to  15  inches,  and  subsequently  restored  inch  by 
inch  to  21  inches,1  and  the  same  explanation  applies  to  every  other 
inch  of  the  scale. 

As  it  is  demonstrable  from  the  certificate  itself  that  the  aneroid  lost 
upon  the  mercurial  barometer  at  every  inch  of  its  scale  when  pressure 
was  diminished,  I  am  unable  to  see  the  propriety  of  applying  as  correc- 
tions the  amounts  which  are  stated  on  p.  51  (in  the  column  headed 
"Correction  to  aneroid  with  a  pressure  diminishing").  For  example,  at 
23,  22,  and  21  inches  it  is  directed  that  there  are  no  corrections  when 

1  It  is  probable   that   this  part  of  the  examination  did  not  occupy  so  much  as 
thirty  minutes. 


54  UPON  THE   USE  OF  THE  ANEROID  BAROMETER 

pressure  is  diminishing,  yet  the  certificate  itself  shows  that  the  aneroid 
lost  0*350  of  an  inch  at  each  of  those  inches  during  the  time  it  was 
under  trial.  From  this  it  will,  I  think,  be  apparent  that  it  is  desirable 
to  make  some  radical  change  in  the  style  of  Certificates  of  Examination. 

§65.  The  last  point  to  which  I  wish  to  draw  attention  is  the  change  in 
index -error  which  occurred  in  this  instrument.  When  No.  899,  Gary,  was 
examined  at  Kew  in  1888  it  had  a  plus  error  of  0*050  in.  at  29  inches, 
when  the  testing  was  commenced  (mere.  bar.  29*000,  aneroid  29*050).  At 
the  termination  of  the  examination  this  was  changed  to  a  minus  error  of 
0-250  in.  (mere.  bar.  29'000,  aneroid  28*750).  The  aneroid  recovered,  and 
by  the  time  it  came  into  my  hands  in  1889  the  error  at  29  inches  was 
+  0*073.  After  my  testing  was  done,  I  retained  the  instrument  for  a  few 
days  to  watch  its  recovery,  and  when  it  left  me  it  had  at  29  inches  a  minus 
error  of  0*179  (mere.  bar.  29*000,  aneroid  28*821).  It  was  continuing  to 
recover,  and,  by  the  time  it  was  first  used  in  the  field,  I  have  no  doubt  it 
was  reading  closely  against  the  mercurial  barometer.  But  when  this  instru- 
ment came  to  me  the  second  time  (in  1890),  after  having  experienced  large 
variations  in  pressure,  its  index-error  at  29  inches  was  —  0*779  of  an  inch 
(mere.  bar.  29*000,  aneroid  28*221).  I  re-tested  it  under  the  air-pump, 
and  found  that  the  major  part  of  the  error  was  carried  along  the  scale.  At 
16  inches  its  index-error  was  -  0*596  of  an  inch  (mere.  bar.  16*000,  aneroid 
15*404).  If  it  had  been  again  kept  at  a  pressure  of  16  inches  for  a  week 
it  would  again  have  lost  a  large  amount,  and  this  time  the  loss,  so  to  speak, 
would  have  been  piled  up  on  the  top  of  the  index-error  ( -  0*596),  and  in 
the  aggregate  would  have  exceeded  a  barometric  inch.  Although  the  change 
in  index-error  was  obvious  on  return  to  London,  it  would  not  have  been  so 
apparent  to  an  observer  in  the  field  unless  he  had  been  possessed  of  the  means 
of  determining  index-errors.  He  might,  and  probably  would  have  continued 
to  apply  the  corrections  stated  upon  the  Certificate  of  Examination. 

The  Kew  certificate  of  No.  899,  Gary,  declares  the  errors  which  were 
remarked  at  each  inch  of  the  scale  of  this  aneroid  in  Oct.  1888,  upon  its 
being  reduced,  inch  by  inch,  as  rapidly  as  possible.  So  long  as  there  was  no 
index-error  at  30  inches,  the  corrections  stated  in  the  certificate  were  proper 
ones  to  employ,  provided  the  aneroid  experienced  exact  repetition  of  the 
same  treatment.  But  they  are  not  the  proper  ones  to  employ  if  the  time 
conditions  are  different,  or  if  there  is  change  in  the  initial  index-error.  In 
the  absence  of  directions  to  the  contrary,  it  may  be  assumed  by  persons  into 
whose  hands  similar  certificates  come  that  the  corrections  stated  in  them  are 
good  under  all  conditions  and  for  all  time  ;  and  I  have  therefore  thought  it 
desirable  to  point  out  the  limited  value  of  this  form  of  certificate,  and  again 
to  dwell  upon  the  necessity  of  workers  in  the  field  being  able  to  re-determine 
index-errors  of  aneroids  at  any  time. 

§  66.  To  determine  the  index -errors  of  aneroids  in  the  field  one 
must  have  recourse  to  the  mercurial  barometer — a  mountain  barometer, 
on  the  Fortin  principle,  by  preference,  if  it  can  be  carried.  Upon  some 
rough  or  prolonged  journeys  it  is  well-nigh  impossible  to  transport 


IN  DETERMINATION  OF  ALTITUDES.  55 

mountain  barometers  in  safety.  It  is,  however,  possible  on  all  journeys, 
of  whatever  nature,  to  carry  graduated  (unfilled)  barometer  tubes  and 
a  bottle  of  mercury.  In  its  simplest  form,  a  mercurial  barometer  can 
always  be  available  ;  and  by  reverting  to  the  practice  of  earlier  travellers 
in  employing  plain  or  graduated  tubes  and  filling  them  on  the  spot1 
one  may  combine  the  accuracy  of  the  mercurial  barometer  with  the 
conveniences  of  the  aneroid. 

During  the  progress  of  the  experiments  which  are  recorded  in  this 
paper,  several  travellers  have  made  important  journeys  upon  which  they 
have  relied  on  aneroid  barometers  for  determination  of  altitude,  and  they 
have  sometimes  said  that  their  aneroid  observations  agreed  very  well  with 
their  boiling-point  observations.  I  find  this  difficult  to  understand,  and  I 
think  that  the  difficulty  will  be  shared  by  the  travellers  themselves  if  they 
will  submit  their  aneroids  to  artificially-produced  diminution  of  pressure 
for  some  length  of  time,  and  note  the  errors  which  they  will  exhibit  upon 
the  mercurial  barometer. 

I  could  not  speak  with  any  confidence  upon  this  matter  if  there 
had  been  an  exception  to  the  general  rule  ;  but  I  repeat  that  through- 
out the  whole  of  my  experiments  in  the  workshop  there  has  been  no 
occasion  upon  which  there  has  been  one,  and  that  every  aneroid,  without 
exception,  which  has  been  submitted  to  diminished  pressure  for  a  month, 
a  week,  or  even  for  a  day,  has  first  lost  in  a  marked  degree  upon  the 
mercurial  barometer,  and  has  recovered  upon  restoration  of  pressure. 

I  invite  those  who  are  able  to  do  so  to  perform  such  experiments 
as  have  been  described  in  these  pages,  to  convince  themselves  of  the 
serious  nature  of  the  mistakes  which  must  be  fallen  into  by  travellers 
and  others  if  they  are  led  to  suppose  that  aneroids  will  exhibit  the 
same  errors  upon  the  mercurial  barometer  at  the  end  of  a  week  or  a 
month  as  they  do  in  a  few  minutes  or  hours  ;  and  also  to  satisfy 
themselves  that  comparisons  of  a  traveller's  aneroids  against  the  mercurial 
barometer,  at  natural  pressure,  upon  return  to  the  level  of  the  sea  after 
prolonged  journeys  in  elevated  regions,  have  not  the  value  which  is  at 
present  assigned  to  them. 

My  best  thanks  are  due  to  the  various  gentlemen  who  have  aided 
me  by  lending  aneroids, — especially  to  Mr.  Louis  Casella  and  to  Mr. 
J.  J.  Hicks  for  the  facilities  that  they  have  rendered  to  an  enquiry 
which  might  have  proved  damaging  to  their  interests.  It  is  to  be  hoped 
they  will  have  their  reward.  I  shall  have  mine  if  the  publication  of 
this  paper  leads  to  the  more  scientific  use  of  a  valuable  instrument. 

1  To  be  done  in  camp,  and  aneroids  to  be  used  when  on  the  march. 

Although  this  is  a  rough  method,  excellent  results  have  been  obtained  by  it 
in  the  past,  and  it  is  likely  to  afford  a  better  standard  for  comparison  than  will 
be  evolved  by  boiling  thermometers.  At  the  best,  the  boiling-water  method  is  a 
circuitous  manner  of  arriving  at  a  result  which  can  be  obtained  with  greater  facility 
and  by  a  smaller  consumption  of  time  in  another  fashion.  See  Travels  amongst  the 
Great  Andes  of  the  Eqitator,  Appendix  B. 


56 


UPON  THE  USE  OF  THE  ANEROID  BAROMETER 


NOTE    UPON    THE    GREENWICH    TABLE    OF    "CORRESPONDING    NUMBERS 
OF    ELEVATION." 

The  table  to  which  I  referred  at  p.  39  (note)  is  intended  to  be  used  for 
the  graduation  of  Aneroids.  It  starts  from  zero  (level  of  the  sea)  and  gives 
3 1  inches  as  the  corresponding  height  of  the  Aneroid  or  corrected  Barometer 
(that  is  the  Mercurial  Barometer  reduced  to  32°  Faht).  This  table  is  given 
(condensed  and  extended)  upon  the  opposite  page.  Many  instrument-makers 
have  followed  it  literally,  and  made  31  inches  their  zero,  or  level  of  the  sea. 

At  the  foot  of  this  Greenwich  Table  the  instructions  are  given  which  are 
reproduced  upon  p.  57  ;  and,  if  they  are  followed,  there  is  no  objection  to 
31  or  even  32  inches  being  made  zero.  But  in  practice  many  persons  find 
it  impossible  to  follow  these  instructions ;  many  others  are  unacquainted 
with  them  ; *  and  yet  more  would  not  follow  them  if  they  were  acquainted 
with  them.  A  considerable  proportion  of  those  who  employ  aneroids  wish 
to  obtain  a  fair  notion  of  their  elevation  above  the  level  of  the  sea  by  mere 
inspection  of  the  height  indicated  by  the  index-needle,  without  reference  to 
"lower  stations,"  or  being  obliged  to  make  computations  of  any  sort.  I 
have  frequently  pointed  out  to  instrument -makers,  and  think  it  may  be 
useful  to  say  here,  that  these  persons  are  unnecessarily  led  into  error  through 
the  zero  being  placed  at  31  inches.  Inasmuch  as  the  mean  Barometer  at  the 
level  of  the  sea,  in  all  parts  of  the  world,  is  much  nearer  to  30  than  to  31 
inches,2  the  adoption  of  30  inches  as  zero  would  be  more  appropriate. 
Should  this  be  done,  the  "  corresponding  numbers "  will  be  those  given  in 
the  following  table  (the  mean  of  atmospheric  temperature  being  50°  Faht.). 


Aneroid. 
Inches. 

Height 
in  feet. 

Aneroid. 
Inches. 

Height 
in  feet. 

Aneroid. 
Inches. 

Height 
in  feet. 

31-000 

-    894 

24-500 

+     5520 

18-000 

+  13,923 

30-500 

-    450 

24-000 

+     6082 

17-500 

+  14,691 

30-000 

0 

23-500 

+     6656 

17-000 

+  15,481 

29-500 

+    458 

23-000 

+     7242 

16-500 

+  16,295 

29-000 

+    924 

22-500 

+     7841 

16-000 

+  17,133 

28-500 

+  1398 

22-000 

+     8454 

15-500 

+  17,998 

28-000 

+  1881 

21-500 

+     9081 

15-000 

+  18,892 

27-500 

+  2372 

21-000 

+     9722 

14-500 

+  19,817 

27-000 

+  2872 

20-500 

+  10,378 

14-000 

+  20,773 

26-500 

+  3381 

20-000 

+  11,051 

13-500 

+  21,762 

26-000 

+  3900 

19-500 

+  11,741 

13-000 

+  22,786 

25-500 

+  4429 

19-000 

+  12,449 

12-500 

+  23,848 

25-000 

+  4969 

18-500 

+  13,176 

12-000 

+  24,952 

1  As  they  are  not  issued  with  the  aneroids. 

2  See  Smithsonian   Miscellaneous  Collections,  153  ;   entitled   Tables  Meteorological 
and  Physical,  section  iv  (hypsometrical  tables),  tab.  xii,  p.  85. 


IN  DETERMINATION  OF  ALTITUDES 


57 


CORRESPONDING  NUMBERS  OF  ELEVATION  IN  ENGLISH  FEET,  AND  OF  READINGS 

OF  ANEROID  IN  ENGLISH  INCHES  (THE  MEAN  OF  ATMOSPHERIC 

TEMPERATURES  BEING  50°  FAHRENHEIT). 


Height 
in  feet. 

Aneroid. 
Inches. 

Height 
in  feet. 

Aneroid. 
Inches. 

Height 
in  feet. 

Aneroid. 
Inches. 

Height 
in  feet. 

Aneroid. 
Inches. 

0 

31-000 

6000 

24-875 

12,000 

19-959 

18,000 

16-016 

200 

30-773 

6200 

24-693 

12,200 

19-813 

18,200 

15-899 

400 

30-548 

6400 

24-512 

12,400 

19-669 

18,400 

15-783 

600 

30-325 

6600 

24-333 

12,600 

19-525 

18,600 

15-668 

800 

30-103 

6800 

24-155 

12,800 

19-382 

18,800 

15-553 

1000 

29-883 

7000 

23-979 

13,000 

19-240 

19,000 

15-439 

1200 

29-665 

7200 

23-803 

13,200 

19-100 

19,200 

15-326 

1400 

29-448 

7400 

23-629 

13,400 

18-961 

19,400 

15-214 

1600 

29-233 

7600 

23-457 

13,600 

18-882 

19,600 

15-103 

1800 

29-019 

7800 

23-285 

13,800 

18-684 

19,800 

14-993 

2000 

28-807 

8000 

23-115 

14,000 

18-548 

20,000 

14-883 

2200 

28-596 

8200 

22-946 

14,200 

18-412 

20,200 

14-774 

2400 

28-387 

8400 

22-778 

14,400 

18-277 

20,400 

14-666 

2600 

28-180 

8600 

22-611 

14,600 

18-143 

20,600 

14-559 

2800 

27-973 

8800 

22-446 

14,800 

18-011 

20,800 

14-453 

3000 

27-769 

9000 

22-282 

15,000 

17-880 

21,000 

14-347 

3200 

27-566 

9200 

22-119 

15,200 

17-749 

21,200 

14-242 

3400 

27-364 

9400 

21-957 

15,400 

17-619 

21,400 

14-138 

3600 

27-164 

9600 

21-797 

15,600 

17-490 

21,600 

14-035 

3800 

26-966 

9800 

21-638 

15,800 

17-362 

21,800 

13-932 

4000 

26-769 

10,000 

21-479 

16,000 

17-235 

22,000 

13-830 

4200 

26-573 

10,200 

21-322 

16,200 

17-109 

22,200 

13-729 

4400 

26-379 

10,400 

21-166 

16,400 

16-984 

22,400 

13-629 

4600 

26-186 

10,600 

21-012 

16,600 

16-860 

22,600 

13-529 

4800 

25-994 

10,800 

20-858 

16,800 

16-737 

22,800 

13-430 

5000 

25-804 

11,000 

20-706 

17,000 

16-615 

23,000 

13-332 

5200 

25-616 

11,200 

20-554 

17,200 

16-493 

23,200 

13-234 

5400 

25-428 

11,400 

20-404 

17,400 

16-372 

23,400 

13-137 

5600 

25-242 

11,600 

20-255 

17,600 

16-253 

23,600 

13-041 

5800 

25-058 

11,800 

20-107 

17,800 

16-134 

23,800 

12-946 

This  Table  is  intended  more  particularly  for  the  graduation  of  Aneroids  with  a  circle 
of  Measures  in  Feet  concentric  with  the  ordinary  circle  of  Barometric  Height  measured  in 
Inches.  The  circle  of  Feet  is  to  be  read  off,  at  the  upper  and  lower  stations,  by  the 
Index  ;  and  the  rule  for  measuring  the  height  will  be  : — Subtract  the  reading  at  the  lower 
station  from  the  reading  at  the  upper  station  ;  the  difference  is  the  height  in  Feet. 

The  Table  supposes  the  mean  temperature  of  the  atmosphere  to  be  50°  Fahrenheit. 
For  other  temperatures  the  following  correction  must  be  applied  :  Add  together  the 
temperatures  at  the  upper  and  lower  station.  If  this  sum,  in  degrees  of  Fahrenheit,  is 
greater  than  100°,  increase  the  height  by  yinnr  Part  for  every  degree  of  the  excess  above 
100°  ;  if  the  sum  is  less  than  100°,  diminish  the  height  by  TTnnr  part  for  every  degree  of 
the  defect  from  100°. 

I 


PART  4.-RECAPITULATION. 


THE    LOSS. 

All  aneroids  lose  upon  the  mercurial  barometer  when  submitted  to 
diminished  pressure.  §§  1-11,  21-24,  26,  28-30,  40,  42,  51,  57-9. 

When  diminished  pressure  is  maintained  continuously,  the  loss  com- 
monly continues  to  augment  during  several  weeks,  and  sometimes  grows 
to  a  very  important  amount.  §§5,  11,  21—24. 

The  most  important  part  of  any  loss  that  will  occur  will  take  place 
in  the  first  week.  §§  21,  25,  26. 

The  loss  which  takes  place  in  the  first  week  is  greater  than  in  any 
subsequent  one.  §§  21,  23. 

A  considerable  part  of  the  loss  which  takes  place  in  the  first  week 
occurs  in  the  first  day.  §§  28,  29. 

The  loss  may  be  traced  in  a  single  hour,  and  in  successive  hours 
upon  aneroids  with  expanded  scales.  §  30. 

The  amount  of  the  loss  which  occurs  is  different  in  different  instru- 
ments. Some  lose  twice,  or  even  three  times  as  much  as  others.  See 
tables  upon  pp.  17,  21-24,  26. 

The  amount  of  the  loss  which  occurs  in  any  aneroid  depends  (1) 
upon  the  duration  of  time  it  may  experience  diminished  pressure,  and  (2) 
upon  the  extent  of  the  reduction  in  pressure.  §31. 

The  loss  that  occurs  at  a  pressure  which  may  be  well  within  the 
range  of  an  aneroid  gives  only  an  imperfect  clue  to  the  loss  which  may 
occur  at  lower  pressures.  It  is  commonly  the  case  for  aneroids  to  lose 
very  largely  indeed  at  the  inferior  limit  of  their  range.  §  31  (note). 


THE    RECOVERY. 

When  pressure  is  restored,  all  aneroids  recover  a  portion  of  the  loss 
which  has  previously  occurred.  §§  16-18,  32-35,  37,  41,  51,  53-5,  60. 

Some  aneroids,  in  course  of  recovery,  gain  more  than  they  have 
previously  lost.  §§  35,  36,  37  (table).  Minus  index -errors  are  some- 
times lessened,  §  33  (table)  ;  plus  index -errors  are  sometimes  increased, 
§§  32,  33  (table),  34  (table)  ;  and  minus  index -errors  are  sometimes  con- 
verted into  plus  ones,  §  33  (table). 


RECAPITULATION.  59 

The  recovery  is  gradual,  and  commonly  extends  over  a  greater  length 
of  time  than  the  period  during  which  diminished  pressure  has  been 
experienced.  §§  16,  32,  37. 

In  aneroids  which  have  been  kept  at  diminished  pressures  for  a  con- 
siderable space  of  time  (a  week  and  upwards),  the  most  important  part 
of  the  amount  that  will  be  recovered  upon  their  experiencing  restoration 
of  pressure  will  be  regained  in  the  first  week.  §§33  (table),  35. 

The  greater  part  of  the  recovery  of  the  first  week  is  usually  accom- 
plished in  the  first  day.  §§  34  (table),  35. 

The  recovery  in  the  first  hour  is  almost  always  larger  than  that  in 
any  subsequent  hour.  §  35. 

TESTING. 

The  errors  which  will  probably  be  exhibited  by  aneroids  during 
natural  variations  of  pressure  may  be  learned  approximately  by  submit- 
ting them  to  artificially  -  produced  variations  of  pressure,  §  19  ;  but  the 
one-hour  test  which  has  heretofore  been  commonly  applied  for  '  verifica- 
tion '  is  of  little  value  except  for  determining  errors  of  graduation,  or  the 
errors  which  will  be  exhibited  at  similar  pressures  in  a  similar  length  of 
time.  §§  20,  49,  65. 

It  is  desirable  that  there  should  be  some  change  in  the  present  form 
of  Certificates  of  Examination,  §§  63-5  ;  and  that  the  change  should  be  a 
radical  one,  §  64. 

ON    THE    ANEROID    AT    FIXED    STATIONS. 

Under  certain  conditions,  an  aneroid  will  not  follow  natural  diurnal 
or  hourly  variations  in  atmospheric  pressure  with  reasonable  accuracy. 
§§  40,  41.  The  index  of  an  aneroid  may  indicate  diminishing  pressure 
at  a  time  when  pressure  is  actually  increasing.  §  40. 


ON    SIMULTANEOUS    COMPARISONS    OF    ANEROIDS. 

Aneroids  left  at  upper  or  lower  stations  (with  the  view  of  applying 
corrections  to  simultaneous  observations  at  lower  or  upper  stations)  cannot 
indicate  diurnal  or  hourly  variations  in  pressure  even  with  approximate 
accuracy  unless  they  have  remained  at  the  level  of  such  upper  or  lower 
stations  for  several  days.  §  42. 


ON    ALTERATION    OF    INDEX-ERRORS. 

The  index-errors  of  aneroids  are  seldom  or  never  constant.     §  49. 


60  RECAPITULATION. 

In  consequence  of  the  difference  between  the  amounts  lost  and  the 
amounts  recovered,  as  well  as  through  other  causes,  the  index-errors  of 
aneroids  are  liable  to  alter  considerably.  §§  16,  17,  35—39. 

A  large  percentage  of  aneroids  gain  under  restoration  of  pressure  a 
greater  amount  than  they  have  previously  lost  under  diminution  of  press- 
ure ;  and  a  large  percentage  recover  less  than  they  have  lost.  It  is 
exceptional  to  find  the  loss  exactly  balanced  by  the  recovery.  §§  36,  37. 
In  some  aneroids  there  is  a  continual  tendency  towards  the  plus,  and  in 
others  towards  the  minus  direction.  §  38. 

Index-errors  generally  pass  along  the  scale  when  aneroids  are  used 
rapidly.  §§  43-45,  65. 

Index-errors  of  aneroids  need  to  be  re-determined  from  time  to  time. 
§§  47-49,  62,  65. 

How  index-errors  may  be  determined.     §  66. 


ON    MEASUREMENT    OF    ALTITUDES. 

It  is  probable  that  large  reductions  will  have  to  be  made  in  the 
height  of  many  positions  which  have  been  determined  by  aneroid.  §  27. 

Reasons  for  this.     §§  21-26,  28-35,  40. 

Ascending  observations  of  aneroid,  as  a  general  rule1  (provided  the 
instruments  are  in  "a  state  of  repose"  when  starting  from  the  lower 
station),  indicate  a  greater  diminution  of  pressure,  or  a  greater  altitude 
than  the  truth.  §§  3-9,  14,  15,  21-31,  40,  52,  57  (table),  58  (table), 
59,  63  (certificate). 

The  error  (due  to  loss  upon  the  mercurial  barometer)  in  the  indicated 
decrease  of  pressure  is  greatest  when  diminished  pressure  (increase  of 
elevation)  has  been  experienced  continuously  for  about  a  month,  pp.  12,  13, 
17  (tables);  §§11,  21-24.  In  altitudes  deduced  from  ascending  observa- 
tions of  aneroids,  errors  are  likely  to  be  greatest  when  the  instruments 
have  been  subjected  continuously  to  diminished  pressure  for  a  month  and 
upwards.  §§  21-26,  48. 

Under  certain  conditions,  ascending  observations  of  aneroid  may  indi- 
cate less  diminution  of  pressure,  or  less  altitude  than  the  truth.  §  55 
(note) 

Provided  the  instruments  are  in  "a  state  of  repose"  when  starting 
from  the  upper  station,  descending  observations  of  aneroid,  as  a  general 
rule,  indicate  a  greater  increase  of  pressure,  or  a  greater  difference  of 
level,  than  the  truth.  §§  12,  55. 

The   error   in   the    indicated    increase    of    pressure   is   greatest   when 

1  There  may  be  exceptions  to  the  general  rule,  arising  from  defects  (such  as  bad 
graduation),  or  accidents  which  are  not  discussed  here. 


RECAPITULATION.  61 

diminished   pressure   has  been   previously    experienced   for   a    month    and 
upwards.     §  55. 

Under  certain  conditions,  descending  observations  of  aneroid  may  indi- 
cate less  increase  of  pressure,  or  less  difference  of  level,  than  the  truth. 

§§57  (see  table,  Col.  5)  ;  60,  64  (see  Col.  3  of  table). 

Descending  observations  of  aneroid  seldom  or  never  agree  with  ascend- 
ing ones.  §  50. 

The  reason  of  this.     §§  53-60. 

To  determine  differences  of  level,  observe  the  differences  of  pressure 
indicated  on  the  scale  of  inches  rather  than  the  differences  in  altitude 
indicated  on  the  scale  of  feet.  §  62. 

Means  of  ascending  and  descending  observations  are  recommended  in 
certain  cases.  §§  61,  62. 

Comparisons  of  travellers'  aneroids  against  the  mercurial  barometer, 
at  natural  pressure,  upon  return  to  the  level  of  the  sea  after  prolonged 
journeys  in  elevated  regions,  have  not  the  value  which  is  at  present 
assigned  to  them.  §  17,  p.  55. 


THE    END. 


Printed  by  R.  &  R.  CLARK,  Edinburgh. 


VOLCANIC   DUSTS, 
FROM  THE  GREAT  ANDES  OF  THE  EQUATOR. 

1.  VOLCANIC  DUST  FROM  COTOPAXI,  Eruption  of  June  26,  1877,  which  fell  at 
Quito  after  an  aerial  voyage  of  34  miles.      See  Travels  amongst  tlie  Great  Andes, 
chapter  vi.     ["  In  the  brown  glass  chips  vactioles  are  abundant,  many  of  them  range 
from  about  *001  to  '002  inch  in  diameter,  but  some  are  still  smaller."     Prof.  T.  G. 
Bonney,  Proc.  Royal  Soc.,  June,  1884.] 

2.  VOLCANIC   DUST  FROM   COTOPAXI,  Eruption  of  July  3,  1880,  which  was 
ejected  to  a  height  of  40,000  feet  above  the  level  of  the  sea,  and  fell  on  CHIMBORAZO 
after  an  aerial  voyage  of  64  miles.     See  Trends  amongst  the  Great  Andes,  chapter 
xviii.     The  finest  particles  Weigh  less  than  one  twenty-five  thousandth  part  of  a  grain. 

3.  VOLCANIC  DUST  FROM  THE  TERMINAL  SLOPE  OF  COTOPAXI,  19,500  feet 
above  the  level  of  the  sea.     This  is  the  matter  which  is  ejected  daily  by  the  Volcano. 
See  Travels  amongst  the  Great  Andes,  chapter  vii. 

4.  VOLCANIC  DUST  FROM  15,300  FEET  ON  COTOPAXI,  about  2000  particles  to 
a  grain.     See  Travels  amongst  the  Great  Andes,  chapter  vii.     ["The  granules  com- 
monly range  from  '01  to   '015  inch  in  diameter.     The  most  abundant  are  minute 
lapilli  of  scoriaceous  aspect  ;  in  less  numbers  are  glassy  whitish  and  reddish  granules 
— with  these  occur  fragments  of  felspar,   augite  and  hypersthene."     Prof.   T.   G. 
Bonney,  Proc.  Royal  Soc.,  June,  1884.] 

5.  LAPILLI   FROM  15,000  FEET  ON  COTOPAXI.     See  Travels  amongst  the  Great 
Andes,  chapter  vii.     ["  Pumiceous  lapilli ;  pulverized  glass  ;  and  mineral  fragments." 
Prof.  T.  G.  Bonney,  Proc.  Royal  Soc.,  June,  1884.], 

6.  LAPILLI  FROM  AMBATO  (8600  FEET).    Mainly  colourless,  vesicular  pumice. 
Many  of  the  fragments  have  entangled  within  them  small  microliths,  and  also  plates 
of  a  pale  greenish  mica.     The  town  of  Ambato  is  built  upon  this  deposit.     See 
Travels  amongst  the  Great  Andes,  chap.  iv.    . 

7.  FINE  VOLCANIC  DUST  FROM  MACHACH1  (9800  FEET),  existing  as  a  con- 
tinuous stratum  ten  inches  thick,  the  product  of  some  unrecorded  eruption  of,  great 
intensity.      Consists  largely  of  felspar  and  hornblende.      The  finest  particles  are 
felspar  and  pumice.      "Almost  as  soft  to  the  touch  as  cottonwool."     See  Travels 
amongst  the  Great  Andes,  chap.  v. 

8.  FINE    PUMICE    DUST   FROM    MACHACHI    (9800   FEET).     This    forms  beds 
many  feet  in  thickness,  and  consists  mainly  of  clear,  colourless,  vesicular  pumice, 
which  includes  greenish   mica,    some   in   minute   hexagonal   plates.      See    Travels 
amongst  the  Great  Andes,  chap.  v. 

These  Volcanic  Dusts  form  most  interesting  and   instructive   objects   for  the 
Microscope. 

Sold  in  bottles,  price  Is.  6d.  each.     Each  sample  contains  one  grain  and  upwards. 


Mr.  Gregory  can  also  supply  fine  and  coarse  dusts  from  ETNA,  Eruption  of  1879, 
collected  by  the  late  Professor  Silvestri,  of  Catania  ;  a  few  specimens  of 
TYPICAL   LAVAS   FROM   COTOPAXI   AND  CHIMBORAZO 

including  the  HIGHEST  ROCK  OF  CHIMBORAZO,  obtained  at  19,300  feet;  and  also 
PUMICE  FROM  PICHINCHA. 

Volcanic  Dust  from  an  eruption  in  St.  Lucia  in  1812,  which  fell  on  board  ship  oflf 
Barbadoes,  price  Is.  6d.  Also  pieces  of  drifted  Pumice  from  Krakatoa,  washed  ashore 
in  Madagascar,  price  Is.  each. 

Any  of  the  Volcanic  Dusts  sent  post  free  by  return  on  receipt  of  Post  order  for 
Is.  7d.,  or  the  set  of  eight  Andean  specimens,  in  box,  post  free  for  10s. 


J.  R.  GREGORY, 
88  CHARLOTTE  STREET,  FITZROY  SQUARE,  LONDON. 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 

This  book  is  DUE  on  the  last  date  stamped  below. 

FinELSchedule:  25  cents  on  first  day  overdue 

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NOV16    1947 


REC'D  LD 

MAY  1 1 1959 


LD  21-100m-12,'46(A2012si6)4120 


\TOR, 


5.8. 
.8. 


O.  SALYIX,  F.R.S.  DAVID  SHARP,  M.B.,  F.R.S.  T.  R.  R.  STEBBING,  M.A. 

And  a  PREFACE  by  EDWARD  WHYMPER. 


HOW  TO  USE  THE  ANEROID  BAROMETER. 

BY  EDWARD  WHYMPER. 
I.  COMPARISONS  IN  THE  FIELD.          II.  EXPERIMENTS  IN  THE  WORKSHOP. 

III.    UPON    THE   USE   OF   THE   ANEROID    BAROMETER   IN    DETERMINATION   OF   ALTITUDES. 

IV.  RECAPITULATION. 
With  numerous  Tables.     To  range  with  "TRAVELS  AMONGST  THE  GREAT  ANDES." 


The  above  three  Works  are  sold  separately. 


CHARLES  SCRIBNER'S  SONS,  743,  745  BROADWAY,  NEW  YORK. 


VJA  7  L  AMOUNT 
I  PAMPHLET  BINDER 


Manufactured  &y 

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Syracuse,  N.  Y. 

Stockton,  Calif. 


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